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Saugeen Conservation warns rising phosphorus levels leading to increase in algae growth in Wilder Lake

golden brown algae covers the bottom of a lake

BY SOUTHGREY.CA STAFF — Flood Warning and Water Quality Coordinator for Saugeen Valley Conservation Authority (SVCA) Shaun Anthony and Water Resources Technician Brittany Taylor presented their message to an audience of cottage owners and residents of Southgate Township on Tuesday, July 9. The group gathered at the Egremont Optimist Community Centre in Holstein where the warning signs that Wilder Lake may be transforming from an oligotrophic to a mesotrophic state were explained.


Oligotrophic, Mesotrophic and Eutrophic lakes

Wilder Lake is currently considered to be a mostly clean and clear oligotrophic lake with low plant growth due to a lack of nutrients in the water. However, phosphorus concentrations have risen over the past several years leading to the recent appearance of golden brown algae, a non-toxic group of aquatic organisms which have the ability to photosynthesize. The intrusion of this algae has made the lake less enjoyable for swimming, boating and fishing. The algae will often rise to the surface of the lake over the course of a day. It can also give an unpleasant smell when decomposing.

The researchers were quick to say that although phosphorus levels remain well within Ontario's acceptable water quality standards, the SVCA was alarmed enough to call the meeting and discuss their findings.

Shaun Anthony and Brittany Taylor

SVCA researchers Shaun Anthony and Brittany Taylor stand beside their presentation display.


"It is probably a combination of many different things," explained Anthony when asked why the lake was showing increased algae production. The shallowness of the lake, the removal of marl during active mining in the early 1900s, warmer temperatures, intense rainfalls, runoff from fertilizers, soaps and detergents as well as septic leaching were all named as possible culprits. While the crowd were very concerned with the root cause, Anthony made it clear that their research had not uncovered the answer to that question.

Wilder Lake Google satellite image

Wilder Lake satellite image: Google.


With no 'smoking gun', he instead offered some best practices for cottagers to help decrease nutrient input and hopefully slow down or perhaps, even reverse the alarming trend:

  1. Pump septic tanks every 3-5 years
  2. Plant native gardens
  3. Limit the size of lawns
  4. Replant trees
  5. Plant rain gardens around driveways
  6. Naturalize shorelines

naturalized shoreline

A well-dressed waterfront with native vegetation and trees absorbs nutrients that might otherwise runoff into the lake.


On the last point, he showed some good and bad examples of cottage shorelines where nutrient runoff was either successfully buffered or unfortunately increased. Naturalized shorelines absorb nutrients before entering the water. Minimizing open access for recreational purposes reduces phosphorus runoff while still providing adequate enjoyment of the lake.

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