Mother Nature has delivered a preview of summer weather in Lethbridge this week.
On that note, crews with the City of Lethbridge are working hard to keep Henderson Lake as clean and pristine as possible.
Officials noted that algae is a common seasonal concern at the lake, with extreme heat worsening conditions and that “it mostly comes down to phosphorous”.
When the lake warms up, the surface water heats while deeper water stays cold, which means the two layers stop mixing, the City explained. Eventually, the cold bottom layer runs out of oxygen and when that happens, the sediments let go of the phosphorous they normally hold on to and it slips back into the water.
Officials said that too much phosphorous lets algae grow faster than the lake can handle. Quick growth creates algae and cyanobacteria blooms. That is more commonly known as blue-green algae and makes the water more harmful to residents and animals.
When the bloom dies, it sucks oxygen out of the water, which causes stressful conditions and can kill fish. The City said it takes several proactive steps to try and avoid dangerous lake algae. Some of these initiatives include:
- Students and staff from Lethbridge Polytechnic sampling and monitoring lake water every two weeks;
- A total of 15 aerators help keep oxygen in the water column. Officials said this assists with water circulation, which supports fish survival;
- Five SolarBees help mix and move the water. The City said these are solar-powered, floating water circulators, which continuously draw water from specific depths and gently distribute it across the surface. This helps prevent stagnation and control blue-green algae;
- The water is treated with Reward, an herbicide that targets excess plant growth that can also result in toxic algae.
Officials noted that more aggressive algae treatments, like copper and pesticides, are not an option because the City does not have a provincial permit to use them.
Additionally, local crews do not dredge the bottom of the lake as it is very expensive and requires extensive permitting that the City does not have.
However, the City is waiting on federal approval for an imported product that targets excessive phosphorous. A decision is expected by mid-June but crews will not be able to use that treatment, if approved, until next spring.
Officials said that means for summer 2026, residents might encounter more instances of algae and cyanobacteria blooms in Henderson Lake. If any significant blooms occur, the City said it will notify residents to help keep them and their pets safe.
