Toxic Algae in Roaring Brook Lake
Cyanobacteria, (also called blue-green algae, toxic algae, and HAB (harmful algal bloom)) are very adaptable and ancient single-celled organisms. In our lake, the NYS DEC has run tests for cyanobacteria and their toxins since 2009, through our participation in the Citizens Statewide Lake Assessment Program (CSLAP). In addition, the Putnam County Department of Health (DOH) has tested for cyanotoxins at our public swimming beaches since 2010.
The DEC has three levels of documentation of HAB: “suspicious”, “confirmed”, and “confirmed with high toxin”. “Suspicious” means that there is the visual appearance of an algal bloom, but without laboratory confirmation. “Confirmed” means that there is laboratory confirmation of the presence of cyanobacteria. Finally, “confirmed with high toxin” means that there is cyanobacteria and that it is producing toxin. It is important to remember that cyanobacteria produce toxin only intermittently (usually during a bloom when dense concentrations of cyanobacteria are multiplying rapidly) and that the toxin is released most abundantly into the water when the cyanobacteria die (often as the bloom disperses). Some conditions that favor cyanobacteria blooms are high nutrient content in the lake and warm, still, dry weather.
We are able to submit samples to the DEC through our participation in the CSLAP (Thank you to our RBL neighbors and volunteer samplers: Bill Brigham, Sam Lee, and Ina Cholst). RBL CSLAP samples showed confirmed blooms in 2012, 2015, 2016, and 2017. There were not many confirmed cyanobacteria from 2009 to 2016 and many of the confirmed samples were negative for toxins. However, in 2017, we sent 6 suspicious samples to the DEC and all were confirmed to be cyanobacteria. Four of the six were producing high levels of toxins.
CSLAP samplings from Roaring Brook Lake over the last few years show the following findings:
|Date||Location||Bloom Status||Microscopic Analysis||Blue-green chlorophyl a concentration (confirmed is above 25 mcg/L)||Microcystin LR (toxin)
(confirmed high toxin is above 20 mcg/L)
|6/7/15||Spur Beach||Confirmed||Anabaena and Woronichinia, with some Microcystis||negative|
|6/28/15||Spur Beach dock||Confirmed with high toxins||Microcystis and Woronichinia||560 µg/L||852 µg/L|
|6/28/15||North Beach||Confirmed with high toxins||Microcystis and
|6/26/16||Shore||Confirmed||Anabaena and Microcystis||190 ug/l||negative|
|6/4/17||South cove (near 159 LSR)||Confirmed||Woronichinia,
Dolichospermum, and Microcystis
|7/4/17||North Beach||Confirmed with high toxins||Dense Woronichinia, and Moderate Microcystis.||706 µg/L||27 µg/L|
|8/27/17||Spur Beach dock||Confirmed with high toxins||Dense Microcystis,
and Trace Dolichospermum.
|1854.8 µg/L||111 µg/L|
|8/27/17||South cove, near 159 LSR||Confirmed||Mod. Dinoflagellates, Microcystis, Radiocystis, Trace Coelastrium, Mougeotia, Woronichinia, Dolichospermum, Fragilaria.||379 µg/L||negative (3.65)|
|9/16/17||South Cove, near 266 LSR||Confirmed with high toxins||Dense Dolichospermum,
|1251 µg/L||64.83 µg/L|
Our CSLAP volunteers do not sample the swimming beaches. This is done separately by the Putnam County Department of Health. In 2017, the DOH closed down one or more RBL beaches because of suspected toxic algae on 18 dates: June 10, 11, 17, 18, July 22 – 28, Aug 14 -18 and Aug 27 – 31, 2017.
It is possible that the increased toxic algae blooms in 2017 reflect greater awareness by the observers and samplers. However, similar increases at other NY State developed lakes during 2017 (but less so in undeveloped lakes), suggest that 2017 weather patterns and increased nutrients play a major role. We can’t easily change the weather, but we can change the nutrient load entering the lake. Each one of us can make a difference. Maintain your septic system, plant a buffer zone, respect wetlands, manage your stormwater.
Be kind to our lake.