Water testing results
Water samples are collected every year at the locations on the map. Your association membership fees and donations pay for the water testing.
Lac Notre Dame August 8, 2024 summary
- Good news that E-coli at all locations is either below detectable levels or just at the detectable level of 10 CFU (Quebec requires below 200 CFU for swimming). Nitrogen and phosphorus levels surprisingly are at the same levels as previous years.
- From Paul Hamilton, consulting biologist: “I suspect the increase in milfoil is related to the spring weather conditions (especially light and water temperature) and nutrients in the sediments. The good news is your nutrient levels do not seem to be bad at all (therefore the washed-in sediments are likely mainly inorganic particles). Stressing the plants (harvesting in the late summer, early fall and in the spring) is the best way to control the growth. Also, poor weather conditions can do the same. For example the water clarity problem you report has two sides, 1) a problem with more nutrients in the lake (with possible blue-green algae) and 2) the visibility will stress the milfoil which may help to control the milfoil later this year (and possibly next year ?) .”
Usher Lake August 15, 2024 summary
- Usher continues to have high nutrient and bacteria levels, with e-coli at 110 CFU at location 11 (below the 200 CFU limit for swimming but well above drinking water recommendations).
Phosphorus levels at location 11 have been higher than the target level of 0.01 mg/l of an uncontaminated lake for the last 5 years. The higher nitrogen and phosphorus levels are somewhat 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
To understand the in-depth results, these Canadian Water Quality Guidelines for the Protection of Aquatic Life provide some target levels.
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.
* Map of water testing locations.
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 100 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.
Prevention: naturalized shorelines, reduced boat wakes, restricted use of fertizers and phosphate-containing detergents
Nitrogen and nitrates - target levels below 0.5. Nitrogen occurs naturally and from fertilizers leaching into the water. High levels make the water unsafe for drinking and upset the natural ecosystem. 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).
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.
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.