Cyanos Activity June 1, 2020

Do not expose yourself or your pets to the water.

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 Monday, June 1, 2020, AER visited Bantam Lake to conduct biweekly cyanobacteria monitoring as part of the ongoing lake management program. Water column profile data and Secchi transparencies 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). 

Integrated water samples were collected at the North Bay and Center Lake sites using a three-meter long sampling tube. Preparations of the samples were similar to preparations discussed in earlier memos (e.g. preserved with Lugols, hydrostatic pressure, etc.) with the following exception. Samples were not concentrated with centrifugation since whole lake water concentrations appeared high. An additional sample was collected in shallow water at the beach in the eastern side of North Bay (aka “Ski Show Beach”) and treated in the same fashion. A concentrated sample was collected with a 10µm mesh plankton net from the Center Lake site. 

Analyses of water samples and Secchi transparency data indicated that a cyanobacteria bloom was occurring at Bantam Lake (Table 1). Cyanobacteria cell concentrations from the three counts ranged from 93,000 to 150,000 cells/mL. Most of the cells (≥95%) were of the filamentous cyanobacteria genus Aphanizomenon spp. (Fig. 1). The State of Connecticut characterizes cyanobacteria cell concentrations of >100,000 cells/mL as Visual Rank Category 3 and recommends several public interventions, including posting beach closure signs (CT DPH and CT DEEP 2019). While a surface scum was not detected, the high cell concentrations resulted in low Secchi transparencies measured from 1.33m at the Center Lake site to 1.87m at the Folly Point site. Additional information on cyanobacteria and recommended public interventions are available at https://portal.ct.gov/DPH/Environmental-Health/Environmental-Health-Section/Blue-Green-Algae-Blooms. 

Of the 24 genera observed in the plankton net sample, six were cyanobacteria and included Aphanothece spp., Dolichospermum spp., Coelosphaerium spp., Microcystis spp., and Woronichinia spp., in addition to Aphanizomenon spp. Six genera of Chlorophyta (aka Green Algae), five genera of Bacillariophyta (diatoms), and three genera of Chrysophyta (Golden Algae) were also observed. 

Aphanizomenon spp. is a cyanobacteria genus comprised of small cells (approximately 5-10µm in length; Fig. 1) arranged in filaments. In the lake, filaments group together in rafts. Once preserved with Lugols Solution, rafts break apart and the individual filaments and cells can be observed under the microscope. This genus is capable of nitrogen fixation and buoyancy regulation. It is also listed as a toxigenic for Cylindrospermopsin, Anatoxin-a, and Saxitoxin (CT DPH and CT DEEP 2019). 

Surface water temperatures increased since May 22nd by 3 to 4°C. The water column was stratified at the North Bay, Center Lake, and Folly Point sites, but not at the South Bay site. The thermocline with the strong resistance to mixing (RTRM ≥ 80) was observed between 4 and 5m of depth at the stratified sites. Oxygen concentrations were >9mg/L at the surface of all sites. Oxygen concentrations at the bottom varied by site (Table 1) with only the bottom of the Center Lake site having <1mg/L.

Literature Cited 

Connecticut Department of Public Health and Connecticut Department of Energy and Environmental Protection. 2019. Guidance to Local Health Departments for Blue–Green Algae Blooms in Recreational Freshwaters. See https://portal.ct.gov/-/media/Departments-and-Agencies/DPH/dph/environmental_health/BEACH/Blue-Green-AlgaeBlooms_June2019_FINAL.pdf?la=en

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