Cyanos Activity June 4 2018

Water is clean for recreation.

Disclaimer: The information presented below reflects conditions throughout the lake and may differ from conditions on specific shorelines. For information regarding beach closings please contact the Torrington Area Health District or local town officials.

On Tuesday June 4, 2018, AER visited Bantam Lake to collect profile data and algae samples as part of the ongoing lake monitoring initiative. Algae samples and profile data were collected from the North Bay Site (N 41.71087° W -73.21155°) and the Center Lake Site (N 41.70056° W -73.22102°). Profile data were also collected at two additional sites (N 41.70773 W -73.22638 and N 41.69015 W -73.22728) to increase the spatial resolution of the monitoring program. The methods discussed in prior memos were employed. 

The concentration of cyanobacteria cells continued to be low with 810 and 1,037 cells/mL observed at the North Bay and Center Lake Sites, respectively. It is important to note that cyanobacteria are increasing in their relative importance within the planktonic algal community. On May 21st at the North Bay and Center Lake Sites, cyanobacteria comprised 8% and 39.7% of the communities, respectively. This week, cyanobacteria comprised 33.8% and 61.1% of those respective planktonic algal communities. 

Woronichinia spp. was the dominant cyanobacteria genera at both sites on June 4th . Others observed in preserved counts or net tow samples included Dolichospermum spp., Coelosphaerium spp., Microcystis spp., Aphanizomenon spp., and Aphanocapsa spp. Golden algae, green algae, and diatoms continued to be important constituents of the pelagic community. The diatom genera Fragilaria spp. and Asterionella spp. constituted 17% and 6% of the community at the North Bay site; however, those genera were absent from Center Lake Site sample. The golden algae genus Dinobryon spp. comprised 17% and 29% of the phytoplankton community at the North Bay and Center Lake Sites, respectively. 

Secchi transparency was good despite very overcast skies; it ranged from 3.37 to 3.62m at the three northern sites (North Bay Site, Center Lake Site, and Site 1). Interestingly, at the southern-most site – across from the State Boat Launch – Secchi transparency was 2.43m. Average Secchi transparency for the lake was 3.20m. 

Surface water temperatures were several degrees warmer compared to May 21st and were 21.2 and 21.6°C across the four sites. Bottom water temperatures at sites where depth was >6m ranged from 14.3 to 15.8°C. At the most southern site where the depth to the bottom is approximately 4.5m, bottom temperature was similar to surface temperature (20.9°C). Results indicated that the lake was stratified with the thermocline and greatest resistance to mixing observed between 4 and 5m depth. 

Oxygen concentrations in waters from the surface to 4m depth ranged from 5.8 to 10.3mg/L. The highly stratified conditions and strong resistance to mixing in the water column has continued to prevent oxygen from being reintroduced to lower depths. Oxygen concentrations at 5m depth at the deep sites ranged from 3.8 to 1.4mg/L. Oxygen concentrations at the bottom of each site, including the shallow southern site, were <1mg/L. As noted in earlier reports, this scenario generally results in the internal loading of nutrients from sediments, which can contribute to high algal productivity if mixed upward.

Data is collected and analyzed by Aquatic Ecosystem Research, who is contracted by Bantam Lake Protective Association.

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