Ware’s Grove Beach

Ware’s Grove Beach at Spofford Lake, shown this summer.

SPOFFORD — Initial tests have determined that the bacteria found earlier this month in Spofford Lake is not the tropical strain that officials initially thought it might be, but the N.H. Department of Environmental Services still advises people and pets to avoid contact with blooms of the bacteria in the water.

The department first issued an advisory on Sept. 10 after lake volunteers alerted officials of a black substance in the water, according to Amanda McQuaid, harmful algal and cyanobacterial bloom program coordinator at DES. At first, officials thought the bacteria might be Lyngbya wollei, a strain of cyanobacteria that is typically found in Florida, but has never been identified in New England, McQuaid said, though it has also been seen in the Great Lakes and Canada.

Based on DES’s recommendation, members of the Spofford Lake Association sent samples of the bacteria to Green Water Laboratories in Florida, McQuaid said in a phone interview Tuesday. The lab determined the bacteria was not Lyngbya wollei, but did identify three other types of cyanobacteria — Stigonema, Scytonema and Tolypothrix — that can produce toxins, McQuaid added.

“It’s not this one type that we were concerned about, which is good,” McQuaid said. “But it’s still a toxic mat of black cyanobacteria that we don’t usually see pop up in New Hampshire lakes.”

The bacteria is currently appearing in the lake as mats, or multilayered sheets, that are rising from the bottom of the lake and washing up along the shoreline, according to an updated DES advisory posted online Tuesday. The testing by Green Water Laboratories found “non-detectable levels” of two toxins in these mats, but McQuaid said there are hundreds of other toxins that could result from these types of cyanobacteria.

“It still could be fairly toxic, just not for certain strains that have already been tested,” she said. “... Even though it’s not exactly what we thought it was initially, it’s still concerning. It’s still a mat of cyanobacteria that could still cause health issues. It’s probably not as toxic as we first thought, but the advisory is the same.”

Cyanobacteria naturally occur in bodies of water worldwide, according to the DES advisory. Blooms of bacteria, like the mats on Spofford Lake, and other types of surface scum, “may form when excess nutrients are available to the water,” according to the department.

DES still cautions people, and especially pets, to avoid contact with the bacteria mats. And while fewer people may be swimming in the lake as the weather cools, McQuaid added that dog owners need to be particularly careful with their pets along the shore of Spofford Lake.

“It’s not likely that anyone would consume this stuff, but dogs especially, could go in the water, get it on their fur, and consume it and become ill from this,” she said. In humans, toxins that result from cyanobacteria can cause health issues ranging from skin irritation, nausea and seizures to long-term liver and central nervous system damage, according to the DES advisory.

The Spofford Lake Association, a nonprofit group dedicated to protecting and sustaining the lake and surrounding watershed, currently recommends against using the water for drinking or showering, according to a post on the organization’s website. But, the association said, it is OK to use lake water for dish washing or irrigation. McQuaid added that swimming in open water is also fine, but people and pets should avoid the mats on the shoreline.

McQuaid said Tuesday that the black mats in Spofford Lake still require further DNA testing to determine what other types of bacteria may be present and what toxins those bacteria may cause. The department is partnering with Keene State biology professor Loren Launen to conduct this testing, which will take several weeks. In the meantime, the DES advisory against coming into contact with the bacteria mats will remain in effect until the department can confirm that they have subsided.

That will take time, McQuaid added, and the best way to get rid of cyanobacteria blooms is to let them die off naturally.

“I know it’s not ideal, but it’s best to leave it alone and let it do its thing,” she said. “Once it’s on your beach, you can certainly rake it, but we wouldn’t want you to handle it. You don’t want to breathe it in. It’s probably very low risk, but we’re still concerned about what this is.”Jack Rooney can be reached at 352-1234, extension 1404, or jrooney@keenesentinel.com. Follow him on Twitter @RooneyReports.

Jack Rooney can be reached at 352-1234, extension 1404, or jrooney@keenesentinel.com. Follow him on Twitter @RooneyReports.