Water Quality Testing Results

Lac Notre-Dame — August 4, 2026

• Water samples were collected at 6 LND locations this year. Please refer to the interactive map of the latest test results.
• We added a new testing location (#15) at Ch. Shaw this year, where a tributary is running under the road and into the lake. The erosion around the inlet is quite obvious, as seen in the image below. The good news is that nutrient and e-coli levels at that new location are very similar to those around the lake. This new location replaces #7 on that same South shoreline.
• Results for nutrients this year are very good and continue to be similar to those from 20 years ago. That’s a bit of a pleasant surprise given all the rain, washing nutrients into the lake in July! For nitrogen, all locations have levels below 0.3 - signs of a healthy oligotrophic lake. Phosphate levels are also in the uncontaminated range at 0.005 to 0.008, similar to results in 2005.
• E-coli results across Lac Notre Dame are also low, again surprising given all the rain the week before testing. 3 locations (#1, #2 and the new #15) had measurements of approximately 30 CFU, while the other 3 locations tested (#4, #6 and #9b) all had less than 10 CFU. These results are all well below the 200 CFU limit for safe swimming.
• We added salts & chloride tests this year - the last time salts were tested was in 2005. Good news - sodium levels this year at 1.7 mg/L are within the same range as in 2005, when they were 1.59 mg/L. Levels are well below the threshold of concern for sodium in drinking water of 20 mg/L.
• More of concern is an 85% increase in chloride from 1.3 to 2.4 mg/L, almost certainly from road chloride usage & septic input around the lake. The largest study on this Salting our freshwater lakes, 2017, PNAS found that lakes with mean chloride above 1 mg/L are disproportionately the ones already on a rising trajectory, long before concentrations get anywhere near the toxicity guideline of 120 mg/L.
• The take-away is to stop this trajectory: 1) maintain your septic system, and 2) avoid road salt and chloride dust suppressant where water can run off into the lake.

Sample collection and analysis by Lisa Fast, with assistance from Carol Doré and Denis Corbeil — thank you!

New location #15 at tributary on Chemin Shaw

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Usher Lake — August 4, 2026

• Water samples were collected at 3 Usher Lake locations this year. Please refer to the interactive map of the latest test results.
• Nutrient results from Usher Lake show a continuing pattern with nitrogen levels in the moderate range (above 0.35) at all three testing locations, indicating a lake in the mesotrophic range. Nitrogen levels above 0.35 at all three Usher Lake testing locations indicate that the lake is in the mesotrophic range. Mesotrophic lakes are known to have intermediate levels of biological productivity and moderate amounts of nutrients such as phosphorous and nitrogen while still hosting diverse and healthy populations of aquatic flora and fauna. Phosphates have risen over the last 10 years, although they’re just outside of the range which encourages algae growth.
• E-coli levels reached 140 CFU at location #11 (at the main inflow to Usher) on August 4, but locations #10 and #12 were at 30 CFU. These levels may be impacted by upstream beaver activity, and could be elevated due to the heavy rains in the days immediately before samples were taken from the lake. None of these levels are close to the 200 CFU maximum for safe swimming, although parents with very young children who are more likely to ingest water may wish to avoid swimming close to location 11, which has had levels above 100 in 2020, 2024 and this year.
• A salt test was added this year at location #11. Sodium was only 1.0 mg/L, slightly down from the 1.6 mg/L measured in 2005. This is a very low level of sodium. Calcium was similarly down to 18.8 mg/l, down from 25 mg/L in 2005. Chloride from roads/septic was unchanged at the low level of 0.6 mg/L. This is an excellent sign that there is almost no chloride contamination of Usher Lake from road salt/dust suppressant.

Samples collected by Rejean Valliant and delivered by Carol Doré — thank you!

© 2026 Lac Notre-Dame and Usher Lake Association