Cyanobacteria Bloom In Marlborough Prompts Hop Brook Warning

SUDBURY, MA — A cyanobacteria bloom in Marlborough's Hager Pond has likely spread to Sudbury, prompting a warning to stay away from the water.

Sudbury health officials on Thursday warned residents and their pets to stay away from Hop Brook due to the algae bloom, which could contain toxins that cause illness, and in severe cases paralysis and death.

"Visitors and pets should not touch, enter, or ingest the water from Hop Brook until further notice," the town's advisory said. "Recreators should not participate in activities where water has scum or discoloration. If pets or humans have contact with the water, they are advised to wash the contacted immediately with clean water. Call your doctor or veterinarian if you or your animals have a sudden, unexplained illness or rash."

Cyanobacteria blooms are common in Massachusetts in late summer due to sunlight and water warming to temperatures that support algae growth. The blooms are also feed off of excess nutrients in the water that can come from rain runoff that contains fertilizers and other organic waste.

Hager Pond on the western edge of Marlborough off Route 20 feeds Hop Brook, which flows into the Wayside Inn area, and roughly due west across Sudbury. The brook flows through natural areas in Sudbury, including Hopbrook Marsh Conservation Land, the Stearns Pond Parcel and Haynes Meadow.