Cyanos Activity September 9, 2019
Reconsider activities and limit exposure 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 September 9th AER visited Bantam Lake to perform monthly water quality
monitoring and biweekly cyanobacteria monitoring as part of the ongoing lake
management program. Samples collected for algal identifications and enumerations were from the North Bay site (N 41.71087° W -73.21155°) and Center Lake
site (N 41.70056° W -73.22102°). A plankton net tow sample, using a 10µm
mesh plankton net, was also collected at the Center Lake site. Samples were
treated, stored, and analyzed following methods discussed in a previous memo.
Water column profile and Secchi transparency data were also collected at the
North Bay Site, the Center Lake Site, as well as at 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).
Cyanobacteria concentrations in samples collected on September 9th were the
highest of the season, ranging from 65,000 to 70,000 cells/mL (Table 1). In
the guidance provided to municipalities (CT DPH & CT DEEP 2019) cyanobacteria concentration from 20,000 to 100,000 cells/mL are equated with Visual
Rank Category 2 with the following interventions recommended:
- Notify CT DPH and CT DEEP
- Increase regular visual surveillance until conditions change
- Consider cautionary postings at public access points
Concurrent with the increasing cyanobacteria concentrations was a decrease in
Secchi transparency. The lake average on September 9th was 1.61m while on
August 26th it was 1.91m.
Aphanizomenon spp. and Microcystis spp. were the dominant cyanobacteria
genera observed at the North Bay site. At the Center Lake site Aphanizomenon
spp. and Dolichospermum spp. were the most abundant. All three genera are
listed as toxigenic genera by the State (CT DPH & CT DEEP 2019).
Water temperatures continued to decrease and ranged from highs of 21.2 to
21.3°C in surface waters at all sites to 20.7°C just above the bottom at the Center Lake site. Oxygen levels were >7mg/L at all depths and at all sites with the
exception of waters nearest the bottom sediments at the North Bay, Center
Lake, and Folly Point sites. Oxygen levels nearest the bottom at the South Bay
site were >9mg/L.
Literature Cited
Data is collected and analyzed by Aquatic Ecosystem Research, who is contracted by Bantam Lake Protective Association.
