Maintenance of Retention Ponds

Jul 6, 2016

Each summer, my office receives many enquiries from residents with questions about the growth of aquatic vegetation and algae on retention ponds in their neighbourhood.

Stormwater retention ponds are used to manage stormwater. A primary benefit is that they can capture large volumes of water quickly, and then release it slowly into soil, air, and sewer, thereby reducing downstream flooding and erosion. They also provide a “sink” for pollutants/sediments washed into the water system by stormwater. Retention ponds provide a place for these pollutants/sediments to settle and help to limit their impact. These ponds also provide a range of other benefits, such as habitat for flora and fauna.

Types of Retention Ponds

The City currently has two types of storm retention basins:

Naturalized Ponds: These types of ponds, which have natural vegetation (grasses, willows, etc) along the shoreline and side slopes, are seen in newer residential developments such as Bridgwater and South Pointe. The intent of these ponds is to use native plantings to simulate a more natural environment that one might find in undeveloped wet lands. Naturalized ponds are currently the City standard for new developments, and there’s evidence that they perform better than conventional ponds in terms of controlling algal blooms, weeds, odors, and goose populations.

Conventional Ponds: The majority of ponds across the City of Winnipeg are conventional in style, and are seen in older residential developments such as Waverley Heights and Richmond Lakes. These ponds have sod side slopes and riparian rip-rap (rock) along the shoreline to provide erosion protection from fluctuating water levels. In general, these type of ponds aren’t built anymore in residential developments.

Treatment of Retention Ponds

Retention ponds are like marshes. In spring, a ‘rotten egg’ smell can occur as snowmelt gets into retention ponds and mixes with stagnant water. In summer, slow-draining bodies of water smell of the fish, animals and plants that live in the pond. Algae may also smell, especially in summer during an ‘algal bloom’, when they grow in abundance. During a bloom, the algae appear as a floating green layer on the ponds.

The City maintains structures in ALL retention ponds (such as pumps, wells, and gates), and treats aquatic vegetation only in conventional ponds when necessary. Naturalized ponds do not receive treatment for aquatic vegetation.

Ponds are inspected regularly during the summer months. Typically, the older the pond, the more nutrients it will contain (i.e. phosphorous and nitrogen). As many of the conventional ponds in South Winnipeg-St. Norbert are of an older design, they contain higher nutrient levels, which results in increased growth of algae and submerged vegetation.

The method used by the City to treat a conventional retention pond depends upon many factors: the pond’s size and depth; temperature of the water; amount of aquatic vegetation; and ease of access for equipment. As treatment is impacted by weather, it can be delayed by rainfall or high water conditions. Based on these factors, the City uses a harvesting barge to cut out the vegetation and/or apply chemical herbicides approved by the Province of Manitoba:

Harvesting: A large paddlewheel driven barge, or harvester, cuts and physically removes the vegetation from the ponds. Since the harvester can work only in water more than two feet deep, it can’t remove vegetation along the shoreline.
Herbicides: A licensed contractor applies chemical herbicides to the water surface of those small or irregularly shaped ponds where the harvesting method is not practical. The contractor also applies an herbicide to the stone edging along the shoreline on public property to treat grasses and weeds.

What Can Residents Do?

Two important steps:

Take action and report it! To report the growth of vegetation on a conventional retention pond, phone 311 or E-Mail 311@winnipeg.ca to report the location of the pond and specific details. The 311 Service Centre will forward your report to the City’s Water Department who will visit the site. If you would like someone from the Water Department to call you back, simply ask for a return call when you file your report.
Residents can help to reduce aquatic vegetation and algae on/around all retention ponds by using less lawn fertilizer and picking up dog waste. These materials contain nitrogen and phosphorus, which serve as nutrients for algae and aquatic vegetation. It’s important to know that in accordance with the Province of Manitoba’s 2008 Nutrient Management Regulation, you must NOT apply fertilizer within three metres (10′) of a pond.

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