Drainage Ponds and Vegetation Growth

I’ve been receiving a few calls recently inquiring why the ‘lakes’ in the Neighbourhoods of Bridgwater / South Pointe and Prairie Pointe are filling in with ‘weeds’.

In the past I’ve written about the significance of these drainage ponds, and the huge environmental benefits of the naturalized native plants. I encourage you to read this overview on how the drainage ponds work: Natural Kidneys

To answer the question about WHY the lakes are filling in with ‘weeds’ – I spoke with the company who builds these drainage ponds. This is the update:

• The vegetation in and around the ponds are not weeds – they are bulrushes and are one of the most effective ways of removing toxins and purifying the water run off. (good details in the Natural Kidneys overview)
• Winnipeg has been experiencing much dryer weather these last few years (2023 – 2025) – causing water levels in all drainage ponds to be low.  Manitoba Hydro has been reporting on the financial impact of lower water levels also. Manitoba’s also experienced an increase in forest fires because of the dry weather.
• When water levels are low – the bulrushes spread and grow – and appear to fill in the drainage ponds.

The graphic below provides an excellent overview of the design of the ponds – and the impact low and high water levels have on the bulrushes.

• When water levels are high – the bulrushes are underwater – and either die or go dormant – resulting in more open water.
• When water levels are low, the bulrushes send out runners and more grow in the pond – resulting in less open water.

Also – see this Drainage Pond Brochure to better understand the science involved. Thank you to the Manitoba Landscape Architect Association for creating this informative brochure.

Stormwater Ponds and Native Grasses