A file photo from 2019 shows a pontoon boat cruising by the boat ramp on Damariscotta Lake in Jefferson. The bacteria levels in Damariscotta Lake are currently dangerous. Credit: Alexander Violo / Lincoln County News

Damariscotta Lake has dangerously high levels of E.coli bacteria, so swim at your own risk.

A test on Aug. 4 by the Midcoast Conservancy put the E.coli number at more than 2,419.5 MPN per 100mL, which is roughly 12 times higher than the U.S. Environmental Protection Agency’s recommended maximum threshold of 190 MPN, which stands for “most probable number.”

A test on Thursday came back lower, but it was still above the EPA’s recommended threshold, Patricia Nease, senior watershed manager with the Midcoast Conservancy, said.

Lakes in Maine have been experiencing high bacteria levels over the past several years. However, it has mostly been cyanobacteria — a kind of blue-green algae that can be fatal to dogs and make humans sick.

The source of the E.coli is still unknown, but the conservancy has sent samples for testing, and results will be back sometime this week, Nease said. The bacteria can come from several sources, including humans, waterfowl and livestock, but the high levels of rainfall in the region lately has added to the risk, since runoff can carry contaminants into lakes.

People infected with E.coli can experience diarrhea, vomiting and stomach cramps for up to seven days, according to the Centers for Disease Control and Prevention. Some more rare forms can cause respiratory illnesses, urinary tract infections or bloodstream infections.

Nease said it’s hard to say how long the elevated levels of E.coli will be in Damariscotta Lake — since there are so many factors that go into determining levels of bacteria in open water, bacteria amounts can fluctuate daily. For now, swimming is at your own risk, she said.

“When recreationally swimming, there’s always kind of an inherent risk associated with swimming in open water,” Nease said.

To mitigate the risk of E.coli infection, the Midcoast Conservancy said to avoid swallowing lake water and swimming after heavy rainfall. To protect lakes against E.coli infections, make sure to not swim if you are ill, shower before and after swimming, wash your hands after using the bathroom and changing diapers, and clean up pet waste within the shoreland area.

Reports of E.coli numbers for Damariscotta Lake have been normal in the past, but cyanobacteria has become a seemingly regular summer occurrence. The  Midcoast Conservancy reported high levels of the bacteria in the lake in June, with previous reports showing outbreaks in 2020 and 2021.

Jules Walkup is a Report for America corps member. Additional support for this reporting is provided by BDN readers.

Jules Walkup reports on the midcoast and is a Report for America corps member. They graduated from the University of Georgia with a degree in journalism and moved to Maine from Tampa, Florida in July 2023.