High levels of microcystis algae were detected at Spy Pond during water sampling performed by the Massachusetts Department of Public Health. Water samples are being collected and monitored on a weekly basis. This Public Health Advisory will remain in effect until cell counts drop to safelevels for two consecutive weeks. This particular type of algae can be toxic if ingested in high doses and can cause skin irritation and a rash after wading or swimming. The Arlington Board of Health strongly advises residents not to swim or stand in the water and especially urges residents to keep pets away from the water.

Microcystis is a cyanobacteria algae that grows naturally beneath or on the surface of many waterbodies.  Under certain conditions (such as warm weather and an abundance of nutrients in the water) the algae may undergo an explosive type of growth that results in dense, floating mats of algae.  This is commonly referred to as an “algae bloom.” 

Contact with high levels of the cyanobacteria algae has beenf ound to contribute to eye, ear, and skin irritation.  Microcystis is different from most other types of algae because it contains and can secrete a toxin into the water.  During an algae bloom, the amount of algae and toxin in the water can become elevated and exposure can be potentially harmful to people and animals.

Health concerns vary depending on the concentrations of microcystis and its toxin, microcystin. Ingestion of elevated concentrations of the algae and its toxin can lead to more serious health effects (e.g. muscle cramps, twitching, and liver damage).

For regular updates please check arlingtonma.gov/health.

You can search for the Massachusetts Department of Public Health's Microcysits Algae Bloom Fact Sheet here.