Retention Pond vs Detention Pond: What’s the Difference?

You have probably seen them in nearly every suburban development, office park, and shopping center across the Chicago area; those ponds tucked behind buildings, alongside parking lots, or at the edges of residential subdivisions. Some always have water. Others are usually dry, filling only during rainstorms. Some look attractive with fountains spraying and landscaped edges. Others look neglected, overgrown with weeds, and covered in green algae scum.

These are stormwater management ponds, and they serve critical functions far beyond aesthetics. They protect properties from flooding, improve water quality before runoff reaches natural waterways, and help communities meet environmental regulations. But not all stormwater ponds are the same, and the differences matter for maintenance, for appearance, and for the people who live and work nearby.

This guide explains the key differences between retention ponds and detention ponds (also called detention basins), what each type requires for proper maintenance, common problems that develop when maintenance is neglected, and how these functional water features can become attractive landscape amenities rather than eyesores.

The Fundamental Difference: Permanent Water vs. Temporary Storage

The core distinction between retention and detention ponds is simple:

Retention ponds hold water permanently. They have a constant pool of water that rises during storms and slowly returns to the normal level afterward, but water is always present.

Detention ponds (or detention basins) are designed to be dry most of the time. They fill temporarily during rain events, hold water to reduce peak runoff, then drain completely through outlet structures, returning to their dry state.

Feature	Retention Pond	Detention Pond (Basin)
Normal water level	Permanent pool	Dry or minimal water
During storms	Water rises above normal	Fills with stormwater
After storms	Returns to normal level	Drains completely
Appearance	Lake-like, always visible water	Grassy basin, dry most of time
Aquatic life	Can support fish and plants	Cannot support permanent aquatic life
Aesthetic potential	High (fountains, landscaping)	Limited when dry
Common locations	Residential communities, corporate campuses	Parking lots, industrial areas

Both types serve the same fundamental purpose of managing stormwater runoff to prevent flooding and protect water quality but they accomplish this goal differently and require different maintenance approaches.

How Retention Ponds Work

Retention ponds, sometimes called wet ponds or retention basins, maintain a permanent pool of water designed to hold stormwater runoff and release it slowly over time.

Design and Function

A typical retention pond includes:

• Permanent pool: The normal water level maintained between storms
• Flood storage volume: Additional capacity above the permanent pool for storm events
• Inlet structures: Where stormwater enters the pond from drainage systems
• Outlet structure: Controls water release rate, often with multiple stages for different storm sizes
• Emergency spillway: Prevents overtopping during extreme events
• Forebay: A smaller settling area near inlets that captures sediment before it reaches the main pond

When rain falls, stormwater flows into the retention pond, raising the water level above normal. The outlet structure releases water much more slowly than it entered, reducing peak flows downstream and preventing flooding. Pollutants settle out as water sits in the pond, and biological processes help break down contaminants before water is released.

Water Quality Benefits

Retention ponds provide significant water quality improvement:

• Sediment settling: Suspended particles drop to the bottom over time
• Nutrient processing: Biological activity reduces nitrogen and phosphorus
• Pollutant removal: Heavy metals and hydrocarbons settle or are absorbed
• Temperature moderation: Water cools before reaching streams (important for aquatic life)

These water quality functions are why retention ponds are preferred by many municipalities for new development; they provide both flood control and environmental protection.

Why Retention Ponds Are Common in Chicago Suburbs

The Chicago metropolitan area has seen extensive use of retention ponds in suburban development since the 1970s. Cook, DuPage, Lake, Kane, McHenry, and Will Counties all have stormwater management ordinances that typically require permanent water quality features for new development.

The flat terrain of northeastern Illinois makes retention ponds particularly practical; the land naturally holds water, and the clay soils common in the region limit groundwater infiltration, making permanent ponds feasible without liners in many locations.

💡 Pro Tip: If you are buying a home in a subdivision with a retention pond, check the HOA documents for pond maintenance responsibilities and assessments. Well-maintained retention ponds enhance property values; neglected ones can become eyesores and breeding grounds for mosquitoes.

How Detention Ponds Work

Detention ponds, also called detention basins or dry ponds, temporarily store stormwater during rain events and drain completely afterward.

Design and Function

A typical detention basin includes:

• Storage volume: The capacity to hold stormwater during peak rainfall
• Inlet structures: Where stormwater enters from drainage systems
• Low-flow outlet: Slowly releases water after storms, often a small pipe or orifice
• Emergency spillway: Prevents overtopping during extreme events
• Turfgrass or vegetation: Covers the basin floor when dry

During a storm, water fills the basin, which may look like a temporary pond or lake. After the rain stops, the outlet structure slowly releases water over hours or days until the basin returns to its normal dry state.

Primary Purpose: Flood Control

Detention basins focus primarily on flood prevention rather than water quality:

• Peak flow reduction: Water releases slowly, preventing downstream flooding
• Volume management: Holds large quantities during intense storms
• Quick recovery: Drains completely, ready for the next event

Because water does not remain long enough for biological processes, detention basins provide less water quality benefit than retention ponds. However, they require less space for equivalent flood storage and work well in areas where permanent water is undesirable or impractical.

Where Detention Basins Are Common

Detention basins are frequently used for:

• Commercial and industrial properties: Parking lots and warehouses
• Roadway projects: Highway and street drainage
• Constrained sites: Where space for permanent ponds is limited
• Retrofit situations: Adding stormwater management to existing development

In the Chicago area, you will see detention basins behind strip malls, adjacent to office buildings, and alongside major roads anywhere development has increased impervious surface and stormwater management is required.

Extended Detention Basins: A Hybrid Approach

Some modern stormwater designs combine elements of both approaches. Extended detention basins hold water longer than traditional detention (24-72 hours rather than just a few hours) but still drain completely between storms. This extended holding time allows some sediment settling and water quality improvement while maintaining the dry condition most of the time.

Extended detention basins may have small wetland areas or micro-pools near outlets that remain wet, creating some habitat value while the main basin stays dry.

Maintenance Requirements: Retention Ponds

Retention ponds require ongoing maintenance to function properly and remain attractive. Without maintenance, they deteriorate into eyesores that can actually worsen water quality and create nuisance conditions.

Essential Maintenance Tasks

Algae Management

Algae growth is the most visible and common problem in retention ponds. Nutrients from fertilizer runoff, goose droppings, and decomposing organic matter fuel algae blooms that turn ponds green, create surface scum, and can produce odors.

Algae management approaches include:

• Aeration systems that improve water quality and reduce algae-promoting conditions
• Beneficial bacteria treatments that compete with algae for nutrients
• Algaecide applications for acute problems (with appropriate permits)
• Nutrient source reduction (buffer plantings, goose management)

For detailed water quality strategies, see our guide on how to keep pond water clear.

Aeration

Aeration adding oxygen to pond water is one of the most effective retention pond management tools:

• Prevents stratification that leads to bottom oxygen depletion
• Reduces conditions that cause odors
• Supports beneficial bacteria that process nutrients
• Improves overall water quality
• Discourages algae growth

For information on aeration systems, see our pond aeration systems guide.

Sediment Removal

Over time, sediment accumulates in retention ponds, reducing storage capacity and water quality function. Forebays should be cleaned every 5-7 years typically, with main pond dredging needed every 15-25 years depending on watershed characteristics and sediment loading.

Shoreline Maintenance

Retention pond shorelines require attention:

• Erosion repair where banks are failing
• Invasive plant removal
• Beneficial plantings to stabilize banks and filter runoff
• Mowing and vegetation management in buffer areas

Outlet Structure Maintenance

Outlet structures must be kept clear of debris and functioning properly:

• Regular inspection for blockages
• Trash rack cleaning
• Structural integrity verification
• Repair of damaged components

Aquatic Plant Management

Some aquatic vegetation benefits retention ponds (nutrient uptake, habitat, shoreline stabilization), but excessive or invasive plants require management. Cattails, phragmites, and other aggressive species can overtake ponds without control.

⚠️ Warning: Neglected retention ponds do not just look bad they can fail to provide designed flood protection, become mosquito breeding habitat, develop severe odor problems, and decrease surrounding property values. Regular maintenance is far less expensive than remediation of severely degraded ponds.

Maintenance Requirements: Detention Basins

Detention basins require less intensive maintenance than retention ponds but still need regular attention to function properly.

Essential Maintenance Tasks

Vegetation Management

The turfgrass or vegetation covering detention basins requires regular mowing and maintenance. Overgrown basins collect trash, harbor pests, and look neglected.

Outlet Structure Maintenance

Outlets are critical for detention basin function:

• Low-flow orifices clog easily with debris and must be kept clear
• Trash racks need regular cleaning, especially after storms
• Outlet pipes should be inspected for damage or blockage
• Emergency spillways must remain clear and functional

Sediment Removal

Sediment accumulates in detention basins, particularly near inlets. Regular removal maintains storage capacity and prevents outlet clogging.

Erosion Repair

Water flowing into and out of detention basins can cause erosion:

• Inlet areas where water enters
• Basin floors where flow concentrates
• Outlet areas where water exits
• Side slopes from mowing and foot traffic

Debris and Trash Removal

Detention basins collect windblown trash, leaves, and debris that must be regularly removed to maintain appearance and prevent outlet clogging.

Structural Inspection

Berms, embankments, and concrete structures require periodic inspection for:

• Settlement or subsidence
• Piping or seepage
• Structural damage
• Animal burrow damage

Common Problems with Stormwater Ponds

Both retention and detention ponds develop problems when maintenance is neglected or inadequate:

Algae Blooms

Cause: Excess nutrients (nitrogen and phosphorus) from fertilizer runoff, goose droppings, grass clippings, and decomposing organic matter.

Effects: Green water, surface scum, odors, oxygen depletion, fish kills in severe cases.

Solutions: Aeration, beneficial bacteria, buffer plantings, nutrient source reduction, proper algaecide application when necessary.

Odor Problems

Cause: Anaerobic decomposition in oxygen-depleted bottom water, often combined with algae die-off.

Effects: Hydrogen sulfide (rotten egg) smell, complaints from nearby residents and businesses.

Solutions: Aeration to prevent oxygen depletion, sediment removal, water quality management.

Mosquito Breeding

Cause: Stagnant water, particularly in poorly maintained detention basins with standing water, or retention pond edges with no circulation.

Effects: Nuisance mosquitoes, potential disease transmission, complaints from neighbors.

Solutions: Aeration to create water movement, mosquitofish stocking (retention ponds), Bti larvicide application, eliminating standing water areas, proper drainage maintenance.

Erosion

Cause: Wave action, runoff concentration, mowing damage, foot traffic, burrowing animals, inadequate vegetation.

Effects: Bank failure, sediment input, loss of storage capacity, safety hazards, unsightly appearance.

Solutions: Bank stabilization, riprap installation, vegetated buffers, erosion control plantings, limiting access.

Sediment Accumulation

Cause: Erosion within the watershed, construction activity, inadequate erosion control on contributing properties.

Effects: Reduced storage capacity, diminished water quality function, shallow water promoting aquatic weeds, outlet structure impacts.

Solutions: Forebay cleaning, dredging when necessary, sediment source control in the watershed.

Invasive Plants

Cause: Seeds carried by wind, water, or animals; intentional plantings that become invasive; existing seed banks in soil.

Effects: Displacement of beneficial plants, reduced open water, management difficulties, diminished aesthetic and ecological value.

Solutions: Regular monitoring, early intervention, mechanical removal, appropriate herbicide application (with permits), replanting with native species.

💡 Pro Tip: Most stormwater pond problems are easier and less expensive to prevent than to correct. Regular maintenance programs catch issues early when intervention is simple. Waiting until ponds become severely degraded often requires costly remediation.

Transforming Functional Ponds into Attractive Features

Stormwater ponds do not have to be ugly. With proper management and enhancement, retention ponds in particular can become attractive amenities that enhance property values and provide enjoyment for residents and visitors.

Fountain Installation

Decorative fountains add visual appeal while providing aeration benefits:

• Create focal points visible from surrounding properties
• Provide pleasant sound of moving water
• Improve water quality through aeration
• Reduce algae by improving circulation
• Increase property values and resident satisfaction

Fountains range from simple floating units to elaborate multi-tier displays with lighting. Selection depends on pond size, aesthetic goals, and budget.

Aeration Systems

Subsurface aeration provides water quality benefits without the visual display of fountains:

• Bottom-mounted diffusers release air that circulates water
• Less visible but highly effective for water quality
• Lower operating costs than fountains typically
• Can be combined with fountains for comprehensive aeration

Beneficial Plantings

Strategic plantings enhance both appearance and function:

• Native shoreline plants: Filter runoff, stabilize banks, provide wildlife habitat
• Buffer zones: Vegetated strips between lawns and water that filter nutrients
• Rain gardens: Planted areas that capture and filter runoff before it reaches the pond
• Emergent wetlands: Shallow planted areas that provide filtration and habitat

Lighting

Landscape and underwater lighting transforms retention ponds into nighttime features:

• Underwater lights in fountains create dramatic displays
• Shoreline lighting defines pond edges and improves safety
• Accent lighting highlights plantings and landscape features
• Timer or photocell controls automate operation

Fish Stocking

Retention ponds can support fish populations that add interest and provide some biological control:

• Largemouth bass and bluegill create balanced sport fish populations
• Grass carp (triploid, with permits) control aquatic vegetation
• Fish provide natural mosquito control
• Stocking creates recreational opportunities in some settings

Walking Paths and Overlooks

Access improvements enhance pond enjoyment:

• Walking paths around pond perimeter
• Viewing platforms or docks
• Benches and seating areas
• Interpretive signage about pond function and wildlife

Who Is Responsible for Stormwater Pond Maintenance?

Understanding maintenance responsibility is essential for ensuring ponds receive proper care.

HOA-Owned Ponds

In residential subdivisions, retention ponds are typically owned by the homeowners association. The HOA is responsible for maintenance, funded through assessments on all homeowners. HOA boards should:

• Budget adequately for routine maintenance
• Establish maintenance contracts with qualified providers
• Plan for major expenses (dredging, structural repairs)
• Communicate pond status to residents

Commercial Property Ponds

Commercial property owners are typically responsible for stormwater features on their property. This responsibility passes to tenants in some lease arrangements, so understanding who maintains the pond is important for property managers.

Municipal Ponds

Some stormwater ponds are owned and maintained by municipalities, particularly those serving public rights-of-way or multiple properties. Municipal maintenance quality varies widely with available budgets and priorities.

Shared Responsibility

In some developments, ponds serve multiple properties with shared maintenance responsibility through easements or maintenance agreements. Clear documentation of responsibilities prevents disputes and ensures maintenance occurs.

💡 Pro Tip: If you serve on an HOA board or manage commercial property with a retention pond, establish a relationship with a qualified pond maintenance provider before problems develop. Regular professional maintenance is far less expensive than emergency remediation of neglected ponds.

Regulatory Considerations

Stormwater ponds exist because regulations require them, and those regulations often affect how ponds can be maintained.

Stormwater Permits

Most stormwater ponds are covered by permits that specify maintenance requirements:

• Minimum maintenance standards
• Inspection frequency
• Record-keeping requirements
• Reporting obligations

Failure to maintain ponds as required can result in permit violations, fines, and required remediation.

Wetland Regulations

Some retention ponds develop wetland characteristics over time. If a pond becomes a regulated wetland, additional restrictions may apply to maintenance activities. This does not mean maintenance stops, it means certain activities may require permits.

Herbicide and Pesticide Regulations

Chemical treatments for algae, aquatic weeds, or mosquitoes require appropriate licensing and often permits:

• Illinois EPA permits for aquatic herbicides
• Applicator licensing requirements
• Notification requirements in some jurisdictions
• Label compliance obligations

Professional pond maintenance providers handle these regulatory requirements, ensuring treatments are legal and properly documented.

Dredging Permits

Major sediment removal (dredging) typically requires permits from:

• Local stormwater authority
• Army Corps of Engineers (if wetland impacts)
• Illinois EPA (water quality certification)

Permit requirements should not discourage necessary dredging; they ensure the work is done properly and disposed of appropriately.

Frequently Asked Questions

What is the main difference between a retention pond and a detention pond?

Retention ponds hold water permanently, maintaining a constant pool that rises during storms and slowly returns to normal afterward. Detention ponds (basins) are designed to be dry most of the time, filling only during rain events and draining completely afterward. Retention ponds look like small lakes; detention basins look like grassy depressions that temporarily fill with water.

Why does my retention pond turn green?

Green water in retention ponds is caused by algae blooms. Algae thrive when excess nutrients (nitrogen and phosphorus) are present, typically from fertilizer runoff, goose droppings, grass clippings, and decomposing organic matter. Solutions include aeration to improve water quality, beneficial bacteria to consume nutrients, buffer plantings to filter runoff, and sometimes algaecide treatments.

How often should stormwater ponds be maintained?

Retention ponds benefit from ongoing maintenance including regular inspections, seasonal aeration operation, periodic algae and aquatic plant management, and annual outlet structure cleaning. Forebays should be cleaned every 5-7 years. Full pond dredging is typically needed every 15-25 years. Detention basins need regular mowing, outlet cleaning, and periodic sediment removal.

Can fish live in a retention pond?

Yes, properly managed retention ponds can support fish populations. Common species include largemouth bass, bluegill, and channel catfish. Fish provide natural mosquito control, add visual interest, and can create recreational fishing opportunities. Detention basins cannot support fish because they drain completely between storms.

Who is responsible for maintaining the retention pond in my subdivision?

In most residential subdivisions, the homeowners association owns and maintains retention ponds, funded through HOA assessments. Check your HOA documents for specific information about pond ownership and maintenance responsibility. If maintenance appears neglected, raise concerns with your HOA board.

Why does the retention pond near me smell bad?

Odors typically result from anaerobic decomposition organic matter decaying without adequate oxygen. This commonly happens when pond water becomes stratified, with oxygen-depleted water at the bottom, or when excessive algae dies and decomposes. Aeration is the primary solution, along with sediment management and water quality treatments.

Can a detention basin be converted to a retention pond?

Converting detention to retention is sometimes possible but involves significant engineering considerations including outlet structure modification, liner installation if soils do not hold water, capacity analysis, and permit amendments. The conversion requires professional design and approval from local stormwater authorities.

Do retention ponds attract mosquitoes?

Poorly maintained retention ponds can become mosquito breeding habitat, particularly in stagnant areas with no water circulation. Properly maintained ponds with aeration, good circulation, and fish populations do not typically have significant mosquito problems. Mosquitofish are highly effective for biological control in retention ponds.

How deep should a retention pond be?

Retention pond depth varies by design, but typical permanent pool depths range from 4-8 feet. Shallower areas promote aquatic plant growth and habitat; deeper areas resist algae and provide fish habitat. Depths over 8-10 feet may develop thermal stratification requiring aeration to maintain water quality.

What is the green scum on top of my retention pond?

Surface scum is typically either algae (either colonial blue-green algae or filamentous algae mats) or duckweed (a tiny floating plant). Both indicate excess nutrients. Algae scum can produce odors and indicate water quality problems. Duckweed, while natural, can completely cover ponds if not managed. Treatment depends on the specific type present.

Professional Stormwater Pond Services

Whether you manage an HOA, commercial property, or municipal facility, professional pond maintenance keeps stormwater features functioning properly while enhancing their appearance and value.

Midwest Pond Features provides comprehensive stormwater pond services throughout the Chicago metropolitan area, including:

• Water quality management: Algae control, aeration, beneficial bacteria programs
• Fountain and aerator installation: Equipment selection, installation, and ongoing maintenance
• Aquatic plant management: Invasive species control, beneficial plantings
• Shoreline restoration: Erosion repair, bank stabilization, buffer establishment
• Routine maintenance: Debris removal, outlet cleaning, vegetation management
• Consulting services: Pond assessment, management planning, regulatory guidance

We work with HOAs, property managers, commercial property owners, municipalities, and golf courses throughout the North Shore, DuPage County, and greater Chicagoland area. Our maintenance programs keep stormwater ponds functioning as designed while transforming them into attractive landscape features.

For information about maintenance programs, see our guide to pond maintenance plans and service contracts.

Contact us at (630) 407-1415 or through our website to discuss your stormwater pond needs. Whether you need ongoing maintenance, want to add a fountain, or face an urgent water quality problem, we can help.