The drawdown has started and we are seven feet below our normal operating depth. We have three feet to go, but by now West Bay and both canals are dewatered and Lakewood Bay is isolated from the lake due to a sill under the North Shore bridge that prevents further draining into the Main Lake. Most docks and boathouse pilings are exposed so now is a good time to take stock of what repairs need to be made or debris that needs to be collected.
Warm weather last week slowed the rate of lake cooling. The red line indicating shallow water did not change from last week to this week, and since we turned off the aerators the water near the bottom has cooled slightly (blue line). The cool and windy weather will accelerate lake cooling and the lines will be meeting soon.
Water clarity is increasing again as the cyanobacteria population decreased since September 11 sampling. Cool weather shifts the population towards diatoms and reduced sunlight means less overall plankton growth as we approach winter. Once the lake is fully drawn down the turbidity will increase due to rainfall and stormwater runoff hitting all the exposed sediment, which will limit how clear the water gets.
Phytoplankton biovolume in Lakewood Bay has decreased a lot since September 11. There is only five percent cyanobacteria present, with 84% of the biomass diatoms, and a 75% decrease in overall biovolume. Diatoms will be the dominant population until next summer when conditions favor cyanobacteria again.
Overall biovolume in Main Lake is slightly above the September 11 population. However, diatoms make up 70% of the population and cyanobacteria only 19%. The cyanobacteria population has been low compared to last year but a lot was on the surface. This winter we will look into why and see if there is anything to be done about it.
West Bay is the only location that saw cyanobacteria biovolume increase during the September 25 sampling, but since the increase was from four to eleven percent the bay continued to be dominated by diatoms.