Water testing results
- With financial support from our members (Association membership fees & donations) and occasional financial support like the La Pêche Green Fund, we test samples of water from the lakes in early August. Thank you to all for the support!
Lac Notre Dame August 12, 2025 summary
- Good news! The water this summer in Lac Notre Dame is very clean and healthy. E-coli at all locations is either below or just at detectable levels.
- Nitrogen and phosphorus levels continue to be in the ‘healthy’ range with little change over the last 20+ years in these nutrients. Keep up the good work everyone on maintaining your septic systems, no fertilizer use, and naturalizing your shorelines to reduce erosion and filter the run-off!
- The rain and high water levels in June and July reduced the light reaching the milfoil - there are very few mats on the surface and less growth, even in shallow areas. Water clarity is considerably higher than last year in 2024, signalling less nutrients in the water to feed milfoil and algae.
- Thank you to volunteers Lisa Fast, Denis Corbeil and Carole Doré for collecting and delivering the water samples to the lab.
Usher Lake August 12, 2025 summary
- Usher has better results than previous years. Bacteria levels, with higher e-coli of 60 CFU at location 10. That is well below the 200 CFU limit for safe swimming.
Usher’s nitrogen and phosphorus levels are expected given the small size of Usher, but do increase the risk of toxic Blue-Green Algae.
View spreadsheet of water testing results by map location
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To understand the in-depth results, these Canadian Water Quality Guidelines for the Protection of Aquatic Life provide some target levels.
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Association volunteers collect water samples at specific locations where water enters and exits the lakes. Note these locations are not the same as the Municipality of La Peche’s test locations referenced in the ABV-7 report.
Understanding water testing results
E.coli bacterium - target levels below 10. E coli can cause severe illness. The presence of E. coli in water is a strong indication of recent sewage or animal waste (beavers, geese!) contamination. For swimming, the safety limit is below 200 CFU (CFU = Colony Forming Units in 100 ml of water), for drinking water it’s below 4 CFU.
Prevention: septic system maintenance, and naturalized/protected shoreline to prevent geese.
Phosphorus/phosphates - target levels are below .005 mg/L. Natural run-off from minerals, erosion and stormwater, and run-off from fertilizers and waste can act as a fertilizer for plants and algae in the lake, and can reduce the oxygen content. Lac Notre Dame is consistently close or within this range.
Prevention: naturalized shorelines, reduced boat wakes, restricted use of fertizers.
Nitrogen and nitrates - target levels below 0.35. Nitrogen occurs naturally and from fertilizers leaching into the water. We report on Total Kjeldahl Nitrogen (TKN) - the sum of nitrogen in bound in organic substances, nitrogen in ammonia (NH3-N) and in ammonium (NH4+-N). Lac Notre Dame locations are usually below 0.35 TKN.
Prevention: naturalized shoreline (no lawn) and zero use of fertilizers.
Transparency/Clarity is an indicator of lake health - clear, more transparent water is a sign of a healthy lake. Water transparency is tested with a Secchi disk. Poor transparency of less than 3 meters can be a warning sign of eutrophication. Lac Notre Dame has never had readings of less than 3 meters but some years readings are below 4m.
2014 ABV-7 Report and recommendations
In 2014, the Municipality of La Pêche, with the Association, worked with ABV-7 to produce a report on the shoreline and water of Lac Notre Dame. The report is in French.
ABV-7 was mandated in June 2014 by the Municipality of La Pêche to characterize the shoreline of Lake Notre-Dame, assess the physico-chemical quality of the water and delimit the milfoil meadows on the lake. This information provided a picture of the current situation in order to slow down the eutrophication of the lake and combat its invasion by Eurasian water milfoil.
Eutrophication is the gradual process of a lake becoming too rich in nutrients like nitrogen and phosphorus. The nutrients feed the cycle of plant and algae growth, which over time, can result in oxygen depletion. Lac Notre Dame was characterized as between oligotrophic and the next stage of mesotrophic.