Montgomery Parks officials are urging residents to use caution, particularly with pets, around Lake Needwood as tests have shown elevated levels of a toxic microcystin that is produced by certain species of blue-green algae.
“We basically have this issue every year,” said Melissa Chotiner, a spokeswoman for the parks department. “When the algae forms, the blossoms create this microcystin. As it gets hotter, more of it forms.”
Swimming is prohibited in the 75-acre lake in Rock Creek Regional Park. Dogs are required to be on a leash and aren’t supposed to swim in the lake, according to Chotiner, but sometimes owners allow them to.
The toxin can harm the liver of humans and pets, and officials say dogs that swim in or drink from the lake are at the greatest risk.
The lake will remain open to boating and fishing, but officials advise that any fish caught in the lake should be eaten only if properly cooked.
The lake is located northeast of Rockville in Derwood. The increased algae bloom is likely caused by excessive nutrients entering the lake via stormwater runoff, according to a parks department fact sheet.