Vegetation & wildlife

Retention ponds are home to a variety of vegetation and wildlife. Each pond will have its own animals, plants and growing seasons, so no two will be exactly alike.


The majority of the vegetation that grows in retention ponds is beneficial, as it can filter potentially harmful nutrients out of the water, preventing them from ending up in our waterways. This naturally-occurring vegetation forms during the summer, due to warmer seasonal temperatures, and dies during the fall from colder seasonal temperatures.

The vegetation growth in retention ponds varies greatly depending on the pond and the weather. Some ponds will show substantial vegetation growth early in the season, some show growth later in the season, and others show little to no growth at all.

While the majority of ponds have a varying quantity of algae throughout the summer, some ponds will grow different types of vegetation below and above the water surface. Aside from algae, the most common forms of vegetation in the City of Winnipeg’s stormwater retention basins are Eurasian water milfoil and duckweed. Duckweed is commonly found in slow moving bodies of water, providing habitat and food to other life forms, while acting as an effective natural filtration system for the pond water.

The City of Winnipeg uses various vegetation management programs to help maintain healthy levels of vegetation in each type of pond. Depending on the type and depth of the pond, we may use a harvester to remove the vegetation and/or apply herbicides approved by the Province of Manitoba.


A large paddlewheel-driven barge – a harvester – cuts and physically removes aquatic vegetation in traditional ponds. Since the harvester can only work in water deeper than two feet, it can't remove aquatic vegetation along the shoreline.


A licensed contractor may apply herbicides to the water surface of traditional ponds where the harvesting method is not practical. The contractor may also apply herbicides to the stone edging along the shoreline on public property to treat grasses and weeds.

Algae concerns

Retention ponds are like marshes. In the spring, a 'rotten egg' odour can occur when the snowmelt mixes with the pond water, which has been stagnant all winter. In the summer, slow-draining ponds can smell of the fish, animals and plants (especially algae) that live in the water. Algae may smell more in summer, during an algae bloom, when they grow in abundance. During an algae bloom, the algae appear as a floating green layer on the retention ponds. After treating the pond with herbicides, the treated plants can also produce odours, as the plants die off and decay.

Lawn fertilizer, yard and animal waste contribute significantly to the growth of algae and vegetation in and around retention ponds. Using less fertilizer and picking up your animal and yard waste can help reduce the algae and vegetation in and around retention ponds.

Residents living adjacent to retention ponds who wish to apply fertilizers to their property should review this Provincial regulation before using any fertilizers.


There are many animals that call the City’s retention ponds home, including muskrats, beavers, fish and birds. Fish can get into the ponds by swimming upstream from a river when water levels are high.

The most common birds you will see in a City retention pond are geese. Feeding geese and other wild birds at retention ponds is not recommended, as it causes the number of birds in the area to grow at an unsustainable rate and can lead to an increase in avian diseases. The City collaborates with the Government of Canada, Province of Manitoba and the Winnipeg Airport Authority on the Urban Goose Working Group. The Group's goal is to reduce risks to human health and safety caused by Canada geese in Winnipeg.

Occasionally, dead fish and animals can be found in retention ponds. Fish deaths can occur from a lack of oxygen in the water or other natural causes. Avian disease is often the cause of death for geese and other birds.

Residents are advised to not handle dead or dying wildlife. Injured or dying wildlife should be reported to the Province of Manitoba. Dead animals found at retention ponds on public property will be collected by the City of Winnipeg. To report a dead animal at a retention pond on public property, please contact 311.

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