A flurry of harmful algal blooms were reported on Seneca Lake this week, marking the beginning of the most intense few weeks of the HABs season in the Finger Lakes.
Seneca had been spared for most of the summer, even as its neighbors — particularly Cayuga, Owasco and Canandaigua lakes — had been reporting dangerous blooms for many weeks.
“On Monday we saw seven blooms, mostly on the southeastern part of the lake,” said Bill Roege, HABs director of Seneca Lake Pure Waters Association.
While winds from the north and west contributed to those outbreaks from Caywood south to Peach Orchard Point, the shift this week to winds from the south means the northern sections of the lake can expect blooms soon, Roege added.
Seneca reported its first bloom this summer in Hector on Aug. 22 — seven weeks after Cayuga reported its bloom.
During that stretch, Cayuga reported 29 blooms with toxin levels exceeding the state’s limit for safe swimming and other recreation. Cayuga had ordered the beach at Taughannock closed as early as July 9.
Experts are puzzled about why for the second straight year Cayuga’s bloom season started nearly two month before Seneca’s.
“That’s a tough question,” said Nate Launer, HABs director at the Community Science Institute in Ithaca. “I’m not sure I could answer that.”
It was no more clear to Seneca Lake expert John Halfman, professor at Hobart and William Smith Colleges. “Blooms happen on sunny, calm days, but not on every sunny, calm day,” he said.
Blooms tend to occur in calm weather after heavy rains have triggered runoff loaded with nitrogen and phosphorus. Blooms tend to break up as soon as winds create choppy water.
Although they are often referred to as blue-green algae because they often look like harmless algae, dangerous blooms are a totally different life form known as cyanobacteria. Low level exposure can cause skin and eye irritation. Heavier doses can cause severe liver damage.
Dogs and other pets are particularly vulnerable.
The state Department of Environmental Conservation has set a limit of 4 ug/L (micrograms per liter) for safe swimming. The DEC classifies blooms that exceed 20 ug/L as “high toxin,” raising the stakes for potential harm to those exposed.
Several types of cyanobacteria are common in the Finger Lakes. The most common is also the most toxic — microcystis — which tends to proliferate from late August through early October. Another common form, dolichospermum, tends to occur earlier in in the HABs season.
CSI has already reported 23 blooms this year with toxin levels that the DEC would classify as “high toxin.” Many of them have occurred in the northern end of the lake.
“This year we’ve had roughly the same amount of blooms as last year, but the big difference is we’ve seen a lot of microcystis-dominated blooms in July,” he added.
In past years, the DEC provided funding so that local groups could send samples to laboratories for special toxicity testing. But it discontinued that program this year.
Instead, the DEC relies on a proxy for toxin testing: checking chlorophyll A levels in suspected samples. If a sample has a chlorophyll A level above 25 mg/L, the DEC considers it a “confirmed” bloom. That level tends to correlate very roughly with the DEC’s recreational limit of 4 mg/L of cyanotoxin, Roege said.
The Finger Lakes have been experiencing HABs for at least the past five years, and they appear to be growing gradually more common and intense.
This was the first year that multiple Finger Lakes reported blooms by June 30. Statewide, 32 lakes and ponds reported blooms in June.
An unusually wet spring created extra runoff that carried nutrients into the lakes. That was followed by an unusually hot summer.
On Hemlock Lake, which supplies water to Rochester, the first reported bloom came June 26. Conesus Lake had a bloom report three days later.
The DEC’s website provides a map of blooms statewide, but it doesn’t provide full details on the type of cyanobacteria found or toxicity levels.
Unlike the other Finger Lakes, Cayuga Lake has access to actual toxin testing, thanks to a lab at CSI, which also posts a detailed chart of its sample results.
Most of the other Finger Lakes reported HABs and had closed beaches to swimmers by by mid-August.
Swimming at Keuka Lake’s Indian Pines Park in Penn Yan was closed July 21.
Skaneateles Lake reported its first bloom Aug. 10, leading to closure of Thayer Park swimming at the north end of the lake.
Owasco Lake reported a flurry of eight blooms Aug. 9-13, most of them on the eastern shoreline on the lake’s north end. The Cayuga County Health Department reported that low levels of cyanotoxin were found in the raw lake water entering Auburn’s water system, but it said filtering prevented measurable levels from reaching the town’s drinking water.
Canandaigua Lake reported more than a dozen confirmed blooms by Aug. 3.
That lake is also contending with reports of a sudsy foam that may contain cyanobacteria. Researchers reportedly have concluded that the foam consists of long chains of sugars called polysaccharides.
Roege said SLPWA has received unconfirmed reports of foam on Seneca Lake. He said the volunteer group plans to study the issue.
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