Cyanos Activity June 18, 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.

There were significant changes in cyanobacteria cells concentrations at the North Bay and Center Lake Sites since June 4th (Fig. 1). Cell concentrations of approximately 800 to 1000 cells/mL on June 4th increased to approximately 6,500 and 5,200 cells/mL at the North Bay and Center Lake sites, respectively. These concentrations comprised 70 and 61%, respectively of the pelagic algal cells counted. In comparison, cyanobacteria cells comprised 34 and 61%, respectively of the pelagic algal community on June 4th . 

The concentrations of cyanobacteria cells and total algal cells were still relatively low being under 10,000 cells/mL which was corroborated by the excellent Secchi transparency at the North Bay and Center Lake sites and at one of the supplemental sites AER added to this study to increase the spatial resolution. Secchi transparency at these sites ranged from 3.2 to 3.5 meters. 

At the most southern site, in the bay were the State boat launch is located, Secchi transparency was approximately one meter less at 2.22 meters. This is the second consecutive Secchi transparency at this site that was notably less than that measured at the other sites. 

Two bloom forming cyanobacteria genera were detected on June 18th; those genera were Dolichospermum spp. and Aphanizomenon spp. The former comprised between 38 and 40% of the pelagic community, while the latter comprised between 7 and 24% of the pelagic community. These two species were the principal species responsible for the very high concentrations recorded last season.

A colonial golden algal genus, Dinobryon spp., and a colonial green algal genus, Gloeocystis spp., were also important taxa and ranged from 7 to 13% and 10 to 11% of the community, respectively. 

As noted earlier, Secchi transparencies were good at the three northern sites (North Bay Site, Center Lake Site, and Site 1) where it ranged from 3.2 to 3.5m. At the most southern site in the bay across from the State boat launch, Secchi transparency was approximately a meter less at 2.22 meters. Average Secchi transparency for the lake was 3.08m. 

Surface water temperatures on June 18th were warmer than those observed on June 4th and ranged between 22.6 and 23.3oC. Bottom water temperature at the North Bay site measured at 6m was 17.9°C. At the deeper Center Lake site, temperature at 7.5m was 15.2°C. 

Oxygen concentrations were generally high in waters from the surface to 5m depth. In those strata, concentrations ranged from a high of 10.2 to 7mg/L. At both sites where dissolved oxygen was profiled, concentrations were <0.03 at 6m and below. Oxygen is clearly being consumed faster than it can be replenished due to the resistance to mix at the thermocline (between 3 and 4m at the North Bay site and between 5 and 6m at the Center Lake site). These conditions might create an internal phosphorus loading phenomenon below the thermocline and should be monitored closely in the months to come. 

In summary, water quality is still good. However, the increasing concentrations of cyanobacteria cells in surface waters merits caution and increased vigilance in the monitoring of the algal community.

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

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