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Lac Notre-Dame and Usher Lake Association

Water testing results

Carole Doré has been volunteering as the Association water tester for years. Thank her when you see her! She collects and delivers the water samples every year at the location on the map. Your association membership fees pay for the water testing.

2020 water testing results summary - Lac Notre Dame on August 10 - Usher Lake August 26th

Phosphate run-off from fertilizers and waste can act as a fertilizer for plants and algae in the lake, and can reduce the oxygen content. Target levels are below .005 mg/L.

Nitrogen and nitrates occur 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). Target levels are between 0.100 to 0.500.

2020: TKNTP Total Nitrogen levels: ranged from 0.23 to 0.29 on Lac Notre Dame which is fairly normal for the lake and within the expected range. Usher Lake levels range from 0.19 to an exceptionally high 0.57 at location 11.

E.coli bacterium that can cause severe illness. The presence of E. coli in water is a strong indication of recent sewage or animal waste (beavers, geese!) contamination. The safety target for e-coli in drinking water is a level of 4 CFU or below (CFU = Colony Forming Units in 100 ml of water). For swimming, the safety limit is 100 - 200 CFU.

Dissolved Organic Carbon (DOC) testing was added this year, as it can be a leading indicator of algae levels and overall lake health. Organic carbon is the result of decomposition of plant or animal material.

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.

Eurasian Milfoil is an invasive aquatic plant that usually grows at depths of 1 to 4 metres and can form a dense carpet on the lake’s surface. This association was founded to fight the harm milfoil caused in the early 2000's - it formed such a dense mat on much of the lake that people weren't able to boat through it at all. It's a Zombie weed - each cut bit can form a new weed so we place buoys to keep boats out of the dense areas.

Biologist Paul Hamilton says about 2019, when native weeds recolonized previously heavy milfoil patches:

"the initiation of growth for the milfoil in the spring was stressed by limited sunlight, and colder temperatures (less likely nutrients). The higher water levels will impede the light getting to the bottom of the lake (a requirement for milfoil spring growth). Then the growth of spring algae further blocked the sunlight and the summer development of the lake started. Again this is good news."

We continue to encourage people to cut milfoil near your shore and remove the cuttings.

View spreadsheet of water testing results by map location

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.

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.

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