Stormwater ponds and wetlands are designed to collect and treat stormwater runoff.

They are constructed to catch polluted runoff from surrounding rooftops, roads, parking lots, driveways, sidewalks and other hard surfaces. Once collected inside the pond, pollutants from runoff sink to the bottom, making the water that flows out of the pond less contaminated. In this way, ponds help protect our wetlands, creeks and lakes by using gravity and plants to filter out pollution.

Why are the ponds so green?

Because stormwater ponds are designed to catch pollutants, they include more nutrients than normal, which allows plants and algae to grow quickly. The plants work together with gravity to clean the pond water. Some plant growth is expected and means the pond is keeping pollutants from going into the lake, creek or wetland downstream.

However, an overabundance of plant and algae growth may inhibit a stormwater pond’s function and degrade the pond’s water quality. More importantly, the degradation of a stormwater pond results in polluting the watershed, or drainage area, around a lake, stream, wetland or pond. This negatively affects water quality, which has an adverse effect on plant and animal life, and decreases the recreational potential for these bodies of water.

Pollutants that could be washed into our ponds include:

• Lawncare products such as fertilizers or pesticides
• Animal debris or waste
• Lawn clippings
• Oils, greases and automotive additives
• Dust and dirt from construction, streets or rainfall
• Wind-blown chemicals

What can I do to limit pollution in our stormwater ponds?

• Pick up or rake up trash, leaves and grass from yards, streets and curbs.
• Never dispose of yard waste (or anything else) into ponds and storm drains. Visit our Yard Waste Disposal page to learn about appropriate disposal options.
• Use phosphorus-free fertilizer and fertilize only as needed.
• Remove trash, leaves and grass from yards, streets and curbs.
• Use biodegradable soaps for outdoor cleaning or car washing.
• Sweep driveways and sidewalks instead of hosing them off.
• Pick up pet waste and dispose of it in the trash.
• Maintain healthy sod and grass to limit erosion. Reseed or re-sod all bare areas to keep stormwater from washing soil particles, which also contain phosphorus, into a storm sewer or pond.

City Responsibility

The City does not treat stormwater ponds or wetlands for algae, weeds, odors or other aesthetic problems; however, the City is responsible for the following tasks:

• Regular inspection of stormwater ponds and pipes located within City-owned property or within drainage or utility easements.
• Removal of sediment accumulation, obstructions and debris that clog stormwater pipes or decrease the volume of ponds to the point they require maintenance.
• Maintenance of the “hydraulic and treatment function” of water resources that are located within City-owned property, drainage or utility easements. This is typically related to the accumulation of sediment.

Please contact the City with the following concerns:

Assistance with repairs
Utilities Division
952-949-8530

Drainage concerns
Engineering Division
952-949-8330

Vegetation management permit application or to report dumping of pollutants
Water Resources Coordinator
952-949-8327

Report dumping of pollutants
See Click Fix

Related Information

Blue Thumb

Minnesota Pollution Control Agency

University of Minnesota Extension

Nine Mile Creek Watershed District