PORTSMOUTH — People are being advised to avoid recreational activities at Upper and Lower Melville ponds in Portsmouth because of a harmful algae bloom, several months after Upper Melville Pond was closed to fishing for a study of “forever chemicals” in stocked fish.

The Rhode Island Department of Health and Department of Environmental Management issued the latest advisory July 21 after water samples collected by DEM and tested by RIDOH’s State Health Laboratories exceeded the advisory threshold for blue-green algae, also known as cyanobacteria.

Officials are advising people to avoid all contact with the water, including swimming, fishing, boating and kayaking. The advisory remains in effect until further notice.

Blue-green algae occur naturally in bodies of water but can produce toxins harmful to people and animals. Officials caution that blooms can move throughout ponds and lakes, so people should avoid contact with affected waters and should not drink untreated water or eat fish caught there.

Pet owners should also keep animals from swimming in or drinking the water.

The latest advisory follows a fishing closure at Upper Melville Pond earlier this year as state and federal officials studied how PFAS — persistent “forever chemicals” — accumulate in stocked fish.

DEM and RIDOH, working with the U.S. Environmental Protection Agency, Roger Williams University and the Town of Portsmouth, began the study in May. Officials said it was the first study of its kind in Rhode Island.

Upper Melville Pond, also known as Thurston Gray Pond, was closed to fishing through July 2 to allow researchers to periodically collect stocked fish, anesthetize them and take small tissue samples for testing. Water and sediment samples were also collected.

The study was prompted by elevated levels of PFAS found in sampling of both Upper and Lower Melville ponds. The ponds were built by the U.S. Navy as drinking water reservoirs for Naval Station Newport and are near the former Melville Fuel Defense Support Point, where PFAS-containing firefighting foam was used.

The current algae advisory is unrelated to the PFAS study.

People who come into contact with water containing harmful algae blooms should rinse their skin with clean water immediately and shower and wash exposed clothing afterward. Pets should be washed with clean water and prevented from licking algae from their fur.

Officials say blooms may appear as bright or dark green scum along the shoreline or thick algae floating on the surface, resembling green paint, pea soup or green cottage cheese.

Water samples will continue to be collected, and the advisory will remain in place until testing confirms that the bloom has cleared and the water is free of toxins and high cell counts.

Suspected blue-green algae blooms can be reported to DEM’s Office of Water Resources at DEM.OWRCyano@dem.ri.gov or 401/222-4700.