Cyanos Activity May 22, 2019

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 Wednesday, May 22, 2019, AER visited Bantam Lake to conduct monthly water quality monitoring and biweekly cyanobacteria monitoring as part of the ongoing lake management program. Water column profile and Secchi transparency data were collected from the North Bay Site (N 41.71087° W -73.21155°), the Center Lake Site (N 41.70056° W -73.22102°), a site west of Folly Point (N 41.70773 W -73.22638), and at a site in the South Bay region of the lake (N 41.69015 W -73.22728). 

Samples for algal identifications and enumerations were collected from the North Bay and Center Lake sites. A plankton net tow sample, using a 10µm mesh net, was collected at the Center Lake site. Samples were treated, stored and analyzed following methods discussed in a previous memo. 

A total of 24 algal genera were observed between the net tow and integrated water samples. The diatoms (Bacillariophyta) were represented by seven genera with Asterionella spp. and Aulocoseria spp. the most abundant. The golden algae (Chrysophyta) and cyanobacteria were both represented by five genera. 

Total cell concentrations were 1,695 and 2,797 cells/mL at the North Bay and Center Lake sites, respectively. These were similar to total cell concentrations in samples collected on May 6th . The cyanobacteria cell concentrations on May 22nd were also similar to those on May 6th. Cyanobacteria cell concentrations on May 22nd were low at 645 and 598 cells/mL at the North Bay and Center Lake sites, respectively. 

The planktonic algal community was mostly distributed between cyanobacteria, golden algae, and diatoms. Relative abundances of those respective taxa were 38, 41, and 14% at the North Bay site and 21, 43, and 30% at the Center Lake site. The most abundant genus was Dinobryon spp. of the golden algae, which comprised 31 and 35% of the algal community at North Bay and Center Lake sites. The second most abundant genus was the cyanobacterium Pseudoanabaena spp., at 23 and 21% of the community at the North Bay and Center Lake sites. 

Average Secchi transparency of 3.25m was modestly greater than the May 6th average of 3.00m. The North Bay site continued to have the greatest Secchi transparency at 3.96m while the South Bay site continued to have the lowest (Table 1). All but the South Bay site exhibited a modest improvement over May 6th levels. 

Some early indications of stratification were observed at three of the four sites, albeit at the very bottom of the water column. The South Bay site was still thermally mixed, however anoxic conditions were encountered at the very bottom. The very bottom of the Center Lake site was also anoxic. Oxygen concentrations just above the bottom measurement were above 7.8mg/L at the Center Lake and South Bay sites. Oxygen concentration at the bottom of the North Bay and Folly Point sites were above the biologically critical threshold of 5mg/L. Much of the water column at all sites had oxygen concentrations of >9mg/L and likely due to high wind speeds the day prior and day of monitoring.

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