Cyanobacteria (Blue-Green Algae)

Cyanobacteria, also known as blue-green algae, are naturally found in many freshwater ecosystems. A combination of excess nutrients, sunlight, and high temperatures can lead to a rapid increase in cyanobacteria, called a “bloom.” Blooms of cyanobacteria generally occur in late summer into the early fall when water temperatures are warmest and an abundance of sunlight and nutrients are available. Some species of cyanobacteria can also produce toxins. These toxins are harmful to people and pets. There are no visual properties of a cyanobacteria bloom that indicate the algae are producing toxins. It is only possible to determine if toxins are present with laboratory tests. If a cyanobacteria bloom is observed, it is best to take caution and stay out of the water to avoid any potential exposure to toxins.

Report a bloom

Please let us know if you've discovered a blue-green algae bloom.

Report a bloom

Click here for more information from RIDOH on cyanobacteria blooms.

The Rhode Island Department of Health (RIDOH) and the Rhode Island Department of Environmental Management (RIDEM) work cooperatively to detect/respond to the presence of cyanobacteria blooms, evaluate the potential risks to the public, and, when necessary, issue health advisories notifying the public of health concerns. The agencies jointly issue health/recreational advisories when conditions indicate a cyanobacteria bloom poses a risk to public health.

Current Advisories

RIDEM is conducting surveillance site visits at lakes and ponds that have a history of cyanobacteria blooms and/or several recreational advisories due to cyanobacteria. (LINK to list?) Sites will be visited every other week this summer and fall to evaluate whether cyanobacteria are present. If cyanobacteria are present and in potential bloom/overgrowth status, a sample will be collected for laboratory analysis of cyanotoxins and the number of cyanobacteria cells.

RIDEM also responds to complaints of cyanobacteria at publicly accessible waterbodies. Pictures and a description of the location can be sent to

Surveillance Lake Name

City Town

Almy Pond


Blackamore Pond


Central Pond


Georgiaville Pond


J.L. Curran Reservoir


Larkin Pond

South Kingston

Little Pond


Mashapaug Pond


Upper Melville Pond


Lower Melville Pond


Slack Reservoir


Spectacle Pond


Stafford Pond


Tiogue Lake


Turner Reservoir


Warwick Pond


Wenscott Reservoir

North Providence

Expected Surveillance Monitoring Dates (Week Of)

  • June 1st
  • June 12th
  • June 26th
  • July 3rd
  • July 17th
  • July 31st
  • August 14th
  • August 28th
  • September 11th
  • September 25th
  • October 9th

Past Advisories

What you should do?

  • Do not swim, play, or fish in water that appears to have a bloom.
  • Do not let your pets swim or play in water experiencing a bloom.
  • If you or your pet comes into contact with waters experiencing a bloom, wash with soap and water immediately.
  • Visit the RI Department of Health's website