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2021-08-23 - Water Test Results Update

Water Quality Committee > 2021-08-23 - Water Test Results Update

On Thursday the results came in for the Toxin Tests done on Tuesday Aug 17th. The results showed a decrease in toxins for the 2 lakes tested. This was surprising because we were expecting an increase in the toxin levels due to the slight drop in water clarity.

Results are as follows:

  • Marl Lake (1st lake) 2.34 µg/L (down from 4.51 µg/L on Aug. 3)
  • Lake Rosalind (2nd lake) 4.70 µg/L (down from 7.66 µg/L on Aug. 3)

Yesterday (Friday Aug 20th) the Algae ID and Numbers Report from samples taken on Aug 3rd arrived with clues as to why there was a decrease in toxin numbers.

The Algae ID showed a very high number of a beneficial Green Algae of the genus Chlorella in both lakes sampled. If you do a search for Chlorella you will find that this algae is used as a nutritional supplement with many benefits for humans. Green Algae (which includes Chlorella) is the basis for the food chain in our lakes feeding the different levels of organisms like other plankton, young fish, crayfish etc. The Green Algae is also consumed by Zebra Mussels in huge amounts (Zebra Mussels do not consume Blue-Green Algae).

When the numbers were crunched from the report it showed the following for the samples taken Aug 3rd.

Marl Lake (1st Lake)

  • There was a total of 7700 cells/mL in the sample.
  • Blue -Green Algae- 4 types combining for 4711 cells/mL or 61% of the sample
  • Green Algae- 6 types combining for 2954 cells/mL, or 38% of the sample (Chlorella was 2800 cells/mL of this total)
  • The remaining 1% were some Diatoms and Protists (all beneficial). This is the first time we see a decrease in the Blue-Green algae below 90% for Marl Lake since the Zebra Mussel invasion.

Lake Rosalind (1st Lake)

  • There was a total of 25000 cells/mL in the sample.
  • Blue-Green Algae- 5 types combining for 6670 cells/mL, or 27% of the sample
  • Green Algae- 7 types combining for 17629 cells/mL, or 72% of the sample (Chlorella was 17000 cells/mL of this total)
  • The remaining 1% were some Diatoms and Protists (all beneficial). This is the first time we see that the B-G Algae are not the dominant algae present in the lakes.
  • One question still remains: What is causing the high numbers of Green Algae????


From the Algae ID and Numbers report we can see that there are definitely 2 blooms occurring in the lakes (B-G and Green). There is also a very strong likelihood that the Green Algae has out competed the Blue-Green Algae since the Algae ID of Aug 3. This would explain the decrease in toxin levels on the Aug 17 toxin report for both lakes.

Chlorella (the main genus of the Green Algae bloom) does not form scums but it does give the water a greenish colour. The surface scums that are present on the calm mornings and days are still the B-G algae (floating to the surface at night) and need to be avoided when swimming.

The problem with any bloom, or blooms in our case, is that if it grows too fast with the hot weather and then crashes it can create an oxygen deficit in the lake causing fish kills and strong odours. This is something that has never happened in our lakes and we hope it never does!

The Water Quality Committee will continue to monitor toxin levels and report back to you with the results as the summer winds down.

So in this very strange year you get to watch the “Battle of the 2 Algae” right from your own dock ... Blue-Green (boooo! ) vs Green (the good guys)

Hey, and do not forget, the good news is that the toxin numbers went down!

Rick Kalte