Stormwater Management Ponds

Stormwater management ponds help manage rain and snowmelt in developed areas. They temporarily hold stormwater, help remove pollutants and debris, and slowly release the water back into local waterways. Learn how stormwater management ponds work, who maintains them and how to safely use areas around these ponds.

On This Page

• How stormwater management ponds work
• Pond maintenance
• Safety around stormwater management ponds
• Fencing and pond design
• Mosquitoes and West Nile virus
• Algae and green water

How do stormwater management ponds work?

Stormwater management ponds collect runoff from local storm sewer systems after rainfall, snowmelt and activities such as watering lawns or washing cars.

In developed areas, roads, driveways, buildings and other hard surfaces prevent water from soaking into the ground. Instead, water flows over these surfaces and into the storm sewer system.

As stormwater flows over roads, lawns and other surfaces, it can pick up pollutants and debris such as:

• Dirt and sediment
• Fertilizers and nutrients
• Grass clippings
• Litter

Stormwater management ponds temporarily hold this runoff. The pond allows pollutants and sediment to settle before the water is slowly released to local waterways.

Who maintains stormwater management ponds?

The person responsible for maintaining a stormwater management pond depends on whether the subdivision has been assumed by the City.

If you live in a new subdivision that has not yet been assumed by the City, the developer is responsible for maintaining the pond.

Once a subdivision has been assumed by the City, Public Works is responsible for maintaining the stormwater management pond.

What maintenance is done after a pond is assumed by the City?

Maintenance needs vary from pond to pond and over time. Work may include:

• Removing debris from the pond and surrounding area
• Maintaining gates and valves
• Stabilizing pond banks

Regular grass cutting is not normally part of stormwater management pond maintenance. These areas are designed to include natural vegetation that helps manage stormwater and contain debris.

Is it safe to use a stormwater management pond?

Stormwater management ponds are not designed or intended for recreational use.

Do not:

• Swim or wade in the pond
• Boat on the pond
• Skate on the pond
• Allow children or pets to enter the pond

Water levels can change quickly during and after storms, and ponds are not supervised or routinely checked for recreational water quality.

Can I skate on a stormwater management pond?

No. Do not skate on stormwater management ponds.

The City does not check the ice thickness on these ponds. Water can continue to flow into the pond during winter, causing the thickness and strength of the ice to change quickly.

Ice that appears frozen may not be safe.

Do stormwater management ponds need a fence?

Not every stormwater management pond requires a fence.

Ponds are designed with safety features based on the site. A pond with a gentle slope of less than 3H:1V may not require a fence when other safety features are in place, such as:

• Warning signs
• Vegetation and barrier plantings
• Safety ledges around the pond

Do stormwater management ponds increase the risk of West Nile virus?

Stormwater management ponds are not typically considered good mosquito breeding sites because water levels change regularly and the ponds are exposed to wind.

However, vegetation and debris can create small areas of standing water where mosquitoes may breed.

Regular maintenance, including debris removal and vegetation control, helps reduce these areas.

Why is the water in the pond green?

Green water can be caused by algae or duckweed. These plants can grow quickly during hot weather and when there are high levels of nutrients in the water.

Excess fertilizer from nearby lawns can contribute nutrients to the pond. Reducing or eliminating lawn fertilizer use can help reduce algae growth.

Duckweed can be a natural part of a healthy pond. It provides food for fish and birds, can help reduce evaporation and may help control mosquito breeding.

Fountains are not an effective way to control algae because they can become blocked by pond vegetation. Chemicals are also not used because they can negatively affect surrounding waterways and habitats.