Cyanos Activity July 2 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.

The concentrations of cyanobacteria cells at the North Bay and Center Lake Sites were 11,192 and 12,425 cells/mL, respectively. These were approximately double the concentrations reported for June 18th (Fig. 1). Additionally, the relative importance of the cyanobacteria in the algal community increased from 70% on June 18th to 88% on July 2nd at the North Bay Site and from 61% to 93% for the same dates at the Center Lake Site. Based on these trajectories, it will be important to continue to be watchful for the formation of blooms. 

AER also visually assess from shore conditions at several of the swimming beaches. One was located in the North Bay on the eastern shore; the other was located in the southern section of the lake across from the State boat launch. Bloom conditions were not observed at either beach. We discussed the algal bloom issues with the lifeguards at the public beach at the north end of the lake; they knew to call the Bantam Lake Protective Association if a bloom is observed. 

Aphanizomenon spp., Dolichospermum spp., and – to a lesser extent – Woronichinia spp. were the most abundant cyanobacteria genera at both sites on July 2nd; collectively, these genera accounted for between 84% and 89% of the algal cells counted (Fig 2). All three genera can form blooms and produce toxins. No other observed genera constituted ≥5% of the total cells counted. 

Despite the increasing cyanobacteria cell concentrations, Secchi transparency continued to be good. Measurements on July 2nd ranged from 2.94m at the North Bay Site to 2 3.40m at Site 3 located west of Point Folly (N 41.70773 W -73.22638). Average lake clarity was 3.17m. These Secchi data were not inconsistent with the cyanobacteria cell concentrations observed, which fell within Visual Rank Category 1 where notification of State agencies and increased surveillance are not yet warranted.1 

The extreme heat over the several days prior to July 2nd, clearly impacted the water column in the first few meters where temperatures were elevated compared to those measured by AER on June 18th and by White Memorial staff on June 26th . At 0.5m temperatures across the four sites ranged from 27 to 27.5°C. The greatest temperature / water density gradient occurred between 1 and 4m, depending on site, where the thermocline had formed. Bottom water temperatures at the North Bay Site and Site 3 where maximum depth was between 6.2 and 6.7m was 19.6 and 19.3°C, respectively. At the Center Lake Site, where maximum depth was 8.05m, bottom temperature was 16.3°C. Bottom temperature at Site 4, where maximum depth was only 4.7m, was 22.1°C. 

Oxygen concentrations in waters from the surface to 4m depth ranged from 7.1 to 9.8mg/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. Concentrations at 5m depth ranged from 3.2 to 5.3mg/L at the North Bay Site, Center Lake Site, and Site 3. At the bottom of Site 4, where maximum depth was 4.7m, the oxygen concentration was 2.9mg/L. Oxygen had been completely consumed from 6m to the bottom at the North Bay and Center Lake Sites. At Site 3 a concentration of 1.6mg/L was recorded at 6m but was 0 at 6.5m. 

Lastly, we observed numerous floating patches of aquatic plants across the surface of the lake. Some reached a square meter in size. It is unknown if this is a regular occurrence and due to weekend recreational boating or a result of a recent herbicide treatment.

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

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