South Portland Parks and Recreation said it found signs of a toxic blue-green algae bloom in Hinckley Park in July. Credit: CBS 13

Damariscotta Lake is the latest body of fresh water found to be home to a blue-green algae that is toxic to humans and quickly fatal to dogs, although not yet in amounts great enough to pose a dire threat, according to a local conservation group.

Midcoast Conservancy had a warning posted on its website on Monday that the Maine Department of Environmental Protection had found early signs of cyanobacteria within the large Lincoln County lake, which covers 4,300 acres in parts of Jefferson, Nobleboro and Newcastle. The organization warned that residents should keep themselves and their pets out of areas where green scum had formed on the shoreline or in other places where the greenish-blue algae was visible.

A pond in South Portland’s Hinckley Park was found last month to be infected with the algae. When the population of this bacteria explodes during an algal bloom it can sometimes produce toxins that, when ingested, can kill dogs in a matter of minutes. It can also poison humans, causing illness and, in rare cases, death. The threat of blue-green algae made headlines last year when three dogs died after swimming in a pond filled with toxic algae in North Carolina. The dogs’ owner posted about the event on Facebook, and her story was shared across the country.

“Do not allow children to play in those areas, do not ingest this water, nor allow your pets to drink this water, and shower after swimming,” the warning on the Midcoast Conservancy website said. “If you live on the South Arm [of Damariscotta Lake] and have a drinking water intake, purchase bottled water for drinking (boiling and reverse osmosis do not remove cyano-toxins) and take brief showers (cyano-toxins can become airborne).”

The conservancy has staff and volunteers monitoring lake conditions. A map on the DEP website shows more than a dozen lakes where the algae have been spotted or the likelihood of contamination is listed as ranging from rare to annual. Fed by human and animal wastes, the algae is more likely to occur due to the unseasonably hot weather this summer, according to the warning.