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 Monday, August 1st, 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 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).
Water samples were collected at the North Bay Site and Center Lake Site for algae and cyanobacteria counts. These included whole water samples and a plankton net tow sample. These were prepared and analyzed as described in our April 15, 2022 memo. Samples for algae analyses were collected thirteen days after the July 19th copper sulfate treatment.
General Conditions
Winds were calm for much of the morning; light winds out of the south did pick up near the end of our time on the water. Skies were overcast. Air temperatures were in the mid-60s °F (https://www.wunderground.com/dashboard/pws/KCT-LITCH9/graph/2022-08-1/2022-08-1/daily). Surface scums were not observed along the shoreline at the State Boat Launch, nor were they observed while on the water. Lake water appeared relatively clear.
Cyanobacteria and Algae Community
A total of 33 algae genera were observed in the plankton net and whole water samples
collected on August 1st. The taxonomic group with the greatest richness (most individual
genera) was the Chlorophyta (aka green algae), at 16 genera (nearly half of the
identified algae genera). Five of 33 genera were Cyanophyta (aka cyanobacteria or
blue-green algae). Those were Aphanizomenon spp., Aphanocapsa spp., Dolichospermum
spp., Pseudoanabaena spp., and Woronichinia spp.
Cyanobacteria continued to constitute most of the cells counted but their relative
abundances and cell concentrations continued to decrease since July 19th. Percent
abundances for cyanobacteria at the North Bay Site and Center Lake Site on August 1st
were 88% and 89%, respectively, and down from 97% to 99% on July 19th and July 22nd.
The August 1st cell concentrations at the North Bay and Center Lake Sites of 8,561 and
10,969 cells/mL, respectively, were the lowest since June 6th (Fig. 1).
Woronichinia spp. continued to be the most abundant cyanobacteria genus as it has
for most of the month of July at both sites. Dolichospermum spp. and Aphanizomenon
spp. were the next most important cyanobacteria genera on August 1st (Fig. 2).
The cyanobacteria cell concentrations both sites were characteristic of Visual Rank
Category 1 conditions. Connecticut’s Visual Rank system, which is based on visual assessments,
characterizes conditions from Category 1 (safe conditions) to Category 3
(conditions that present great enough health risk from cyanobacteria to warrant beach
closure signage; (CT DPH & CT DEEP 2021). The State guidance document also provides
categories of cyanobacteria cell concentrations that correspond with each Visual
Rank category (Fig. 1), and recommendations to municipal health departments public
on interventions for Category 2 and 3 conditions, but not for Category 1.
Secchi Disk Transparency and Relative Phycocyanin Concentrations
Two other related indicators of cyanobacteria productivity regularly measured at Bantam
Lake are Secchi disk transparency (surrogate of water clarity) and the surface-to-3
meters average relative phycocyanin concentration (surrogate of cyanobacteria biomass).
Secchi disk transparencies measured on August 1st were between 2.51 and 2.76
meters (Table 1) and have improved since the copper sulfate treatment of July 19th (Fig.
3). Relative phycocyanin concentrations have correspondingly decreased since the
copper sulfate treatment (Fig. 3). The August 1st average relative phycocyanin concentration
was the lowest observed since June 6th.
Water Column Conditions
The water column was stratified at the North Bay, Center Lake, and Folly Point sites.
The thermocline at all three sites was located between 5 and 6 meters of depth. The
upper metalimnetic boundary was detected above the thermocline at the North Bay
and Center Lake sites. Oxygen concentrations at or below the upper metalimnetic
boundary or at and below the thermocline were <1.0 mg/L (Table 1).
The water column was mixed at the South Bay site and the oxygen concentration at
the bottom of the water column was 4.0 mg/L.
Literature Cited
Connecticut Department of Public Health and Connecticut Department of Energy and
Environmental Protection. 2021. Guidance to Local Health Departments for Blue–Green
