Water Resting Results

Notre-Dame Lake - 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.

• Water samples are collected every year at the locations on the map. Your association membership fees and donations pay for the water testing.

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

• All water testing results by date and location for E-coli, phosphates and nitrogen from 2005 (Google Sheet)

• Association volunteers collect water samples at specific locations where water enters and exits the lakes.

• Map of water testing locations.

Understanding water testing results

To understand the in-depth results, these Canadian Water Quality Guidelines for the Protection of Aquatic Life provide some target levels.

• 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 from gathering and excess rain run-off.
• 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 4 meters.

2014 ABV-7 Report and Recommendations

• In 2014, the Municipality of La Pêche and the Lake Association, commissioned the consulting firm ABV-7 to study the shoreline and water quality of Lac Notre-Dame. The report is available at the following links:

  • Download the full report (PDF) in French

  • Download the full report (PDF) in English (translated by DeepL)

• ABV-7 was commissioned to characterize the shoreline of Lake Notre-Dame, assess the quality of the water and chart the milfoil meadows on the lake. The purpose of this study was to better understand the state of the lake in order to combat its invasion by Eurasian watermilfoil.

• The study provides detailed information about eutrophication, which is the process of lake aging. As lakes age, they become increasingly rich in nutrients like nitrogen and phosphorous, a condition that encourages the growth of aquatic plants including the invasive Eurasian watermilfoil.

• The eutrophication process modifies lake characteristics, causing sediment and organic matter build-up, reduced oxygen levels in the water, and a shift in plant species composition. This process can play out over a geological timeframe (i.e. thousands of years). It can also be accelerated by human activity including urbanization, septic system failures, recreational activities and climate change.

Stages of Eutrophication

• According to the ABV7 report, Lac Notre-Dame, originally an oligotrophic lake with clear, well-oxygenated waters and low nutrient levels, is showing signs of eutrophication. The lake’s condition is shifting towards mesotrophy, as indicated by water quality data such as E. coli levels (2-10 CFU/100 ml), total phosphorus concentration (0.015 mg/L), water transparency (4-5 m), and dissolved oxygen saturation (<54%).

• Phosphorus is identified as the main nutrient responsible for the eutrophication of Lac Notre Dame, with sources including natural inputs (wetlands, erosion, organic matter decomposition) and anthropogenic inputs (stretches of shoreline with no vegetation to filter nutrients from runoff into the lake, septic systems, phosphate-rich products, and fertilizers). ABV7 recommendations to combat eutrophication include enforcing shoreline protection regulations, revegetating degraded shoreline areas, controlling phosphorus inputs, and educating residents on good water protection practices.