Cyanos Activity July 19, 2022

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 Tuesday, July 19th, AER visited Bantam Lake to conduct biweekly cyanobacteria monitoring as part of the ongoing lake management program. Water column profile data, total depth measurements, 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).

A plankton tow sample using a 10μm mesh plankton net was collected at the Center Lake site. The concentrated plankton sample was transferred into a 25mL glass amber bottle and stored at 3°C. Approximately 500mL of the top three meters of water column was integrated and collected for algae counts at both the North Bay and Center Lake sites using a three-meter-long sampling tube. Those samples were preserved with Lugol’s solution shortly after collection and stored at 3°C.

A portion of the live phytoplankton in the net sample was carefully examined with microscopy on the same day it was collected to identify and list all algal genera present prior to any treatment or preservation. The integrated whole water samples were pre-pared and analyzed as described in our April 15, 2022 memo.

The data and sample collections occurred just prior to the copper sulfate treatment which was scheduled to occur on the same day.

General Conditions

Light winds were generally out of the south / southwest and skies were bright with passing clouds. Air temperatures during our time on the lake were in the 70s °F (White Memorial Conservation Center - KCTLITCH9). Surface scums were not observed at the State ramp at the time of launching, nor were they observed while on the water. Lake waters did appear somewhat turbid.

Cyanobacteria and Algae Community

A total of 23 algae genera were observed between the net tow and concentrated whole
water samples. Cyanobacteria genera included Aphanizomenon spp., Aphanocapsa
spp., Dolichospermum spp., Microcystis spp., Planktothrix spp., and Woronichinia spp.
The Chlorophyta (aka green algae) were represented by eight different genera, but
none were a major factor in algal community cell concentrations.

The most abundant taxon was the cyanobacteria. Cell concentrations of 106,577 and
115,399 cyanobacteria cells/mL were determined for the North Bay Site and Center
Lake Site, respectively, which represented approximately 99% and 98% of all cells
counted at the respective sites. Cyanobacteria concentrations at both sites were
within the range that characterizes Visual Rank Category 3 conditions. Connecticut’s
Visual Rank Category system characterizes conditions from Category 1 (good conditions)
to Category 3 (conditions that present great enough health risk to warrant beach
closure signage; (CT DPH & CT DEEP 2021). In addition to the beach closure signage,
the State recommends for Category 3 conditions the notification of the CT DPH and
CT DEEP, and increased surveillance.

Cell concentrations at the North Bay and Center Lake sites continue to be characteristic

of the exponential growth phase for cyanobacteria (Fig. 1). The most abundant genus

in the samples from both sites was Woronichinia spp., followed Aphanizomenon

spp. (Fig. 2). Cells of both genera are generally small. Woronichinia spp. colonies are

roundish with cells on the periphery. Aphanizomenon spp. are arranged in filaments

with cells attaching to each other in a linear fashion. Filaments often group together to

form rafts.

Water Column Conditions

The water column was stratified at all sites. At the North Bay and Center Lake sites,

the thermocline was observed between 3 and 4 meters of depth. At the Folly Point and

South Bay sites, the thermocline was lower in the water column. Oxygen concentration

at the bottom of the South Bay site was 3.6 mg/L; at the other three sites, levels

were <1 mg/L from 5 or 6 meters of depth to the bottom (Table 1).

Secchi Disk Transparency and Relative Phycocyanin Concentrations

Two other indicators of the cyanobacteria productivity regularly measured at Bantam

Lake are Secchi disk transparency (surrogate of water clarity) and relative phycocyanin

(surrogate of cyanobacteria biomass). Measurements on July 19th were consistent with

the increased cyanobacteria cell concentrations. Secchi disk transparencies were the

lowest of the season while relative phycocyanin levels were the highest of the season

(Fig. 3).

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

Literature Cited

Connecticut Department of Public Health and Connecticut Department of Energy and

Environmental Protection. 2021. 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/2021/Guidance-to-

LHD-for-Blue-Green-AlgaeBlooms_June2021_FINAL.pdf