Samples were collected on Saturday, August 13, 10 a.m. and noon. Nine sites were tested for fecal coliforms, colour, turbidity, pH, and phosphorus. The samples were taken 10 m from shore.
Three sites far from shore were tested for chlorophyll-A and dissolved organic compounds, both of which give information about the effect of rotting organic material on water quality. Taken together, levels of chlorophyll-A, dissolved organic compounds, and phosphorus tell us about the amount of nutrients in the lake.
Furthermore, three sites were tested for cyanobacteria.
SUMMARY OF 2016 RESULTS
Fecal Coliforms
Fecal counts are 50% higher than 2014-2015, which were unusually high (This year, the average per sample is 13.8, as opposed to the cumulative average of 3.91 for all years).
High coliform counts can be associated with rains (sometimes heavy rains) just prior to testing day: 2016 was a rainy summer. Records indicate 29 mm of rain from 11 to 13 August, but the reason for the increase remains to be established.
According to Public Health norms, untreated lake water is not safe to drink. However, it is still in the “Excellent” range for swimming. Public health norms state that drinking water should have zero coliforms, whether fecal or otherwise. Our lake tests measure only fecal coliforms.
Household tests provide information about other coliforms. It is recommended that lake water be treated by boiling or with a UV filter system before drinking.
Phosphorus
Phosphorus concentration indicates the amount of nutrients reaching the lake through runoff (This is linked to the risk for algae blooms). After four years of low levels, phosphorus concentrations were moderately high last year, and again this year. If this persists, it will be a cause for concern.
Chlorophyll A and Dissolved Organic Carbon
The levels of chlorophyll-A and dissolved organic compounds are based on three samples taken far from shore. The concentration of chlorophyll-A indicates the abundance of phytoplankton (microscopic plants) which are more common if phosphorus levels are high, if the weather is hot, and if water moves slowly. This year, the tests average 2.52 µg/l, which is excellent (but higher than the cumulative average by 40%).
The quantity of dissolved organic carbon tracks the effects of rotting vegetation and animals. Dissolved organic compounds give a brown colour to water. The average for Lake Anne this year is relatively low at 3.8 mg/l. It has remained unchanged in the last four years.
Colour and Turbidity
Colour can be caused by natural minerals, vegetable matter, or other organic compounds. There was a slow increase in colour until 2008, when it appeared to level off. There was a spike in 2015, when it was more than twice as high as the previous years. This year, with a level of 29.4, it is higher than the cumulative average (24.2), but less than last year (41.3).
Turbidity levels above 5 are not a problem for swimming, but untreated water at sites above the norm may not be potable (even without coliforms). Last year, the average turbidity level was 5.66, with 4 sites above the norm. This year, it has gone down to 3.86, with no site above the norm.
pH
Water is acid below a pH of 7 and alkaline above that number. This year, the pH is 7.25. Overall, there is a trend towards slowly increasing alkalinity, except for the last two years.
Cyanobacteria
There were 3200, 1998, and 2111 cyanobacteria/ml at the three sites tested. These sites were chosen because they experience less water movement than the lake as a whole, therefore they are the kinds of areas in which cyanobacteria can proliferate. Results showed a low count that is not a cause for concern.
As mentioned previously, we took these samples in order to measure trends. The presence of cyanobacteria in a lake is normal. Problems arise when their density is too high, at which point they produce algae blooms.
The microbiologist said that said the following changes are worth reporting immediately (to Madeleine or Jérôme):
- Dead frogs in the lake, because frogs are particularly sensitive to cyanobacteria.
- An unusual or rapid increase in algae growth, or of cloudy water resembling broccoli or pea soup.
Conclusion
This year, three measures are higher than average: fecal coliforms, phosphorus, and colour. These changes suggest an increase in dissolved organic substances and material in suspension in the water. These are all associated with a risk for algae blooms. It is too soon to say whether this is a trend, but, if these measures stay at these levels, this will be a cause for concern.
We have a healthy lake where we can swim safely. We will continue to monitor the health of the lake, so that we can be proactive.
What we can do to keep Lake Anne healthy
We can help maintain the health of our lake by following these guidelines:
- Septic systems need to be cleaned regularly (every two years for frequent residents, every three years for weekenders). They also need to be verified to make sure there are no leaks and leaching fields are functional.
- By regulation, the first 15 m of shore line should be covered in bushes and trees to absorb nutrients. Lawns promote run-off which adds to the phosphate load in the lake. Avoid churning up the nutrient-rich sediments lying on the bottom of the lake.
- Avoid fertilizers, especially on lawns and steep hills, and anywhere near the lake.Use only phosphate-free detergents (both for dishwashers and washing machines).
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