Cyanobacteria, also known as blue-green algae, grow naturally in many water bodies. When certain conditions are present, such as warm weather and an abundance of nutrients in the water, the algae may undergo an explosive type of growth that is sometimes called an algae bloom. These blooms look like mats or thick paint on the surfaces of water. Blooms frequently appear blue or green but sometimes appear brown or red. These blooms can be harmful to people and animals.

The danger of cyanobacteria

Contact with cyanobacteria can cause skin and eye irritation. Ingesting small amounts can cause gastrointestinal symptoms. Ingesting large amounts may cause liver or neurological damage. Small children and pets are more susceptible to the effects of cyanobacteria than adults. Dogs, in particular, can get very ill and even die from ingesting cyanobacteria, either by directly ingesting it or licking it off their fur.

What you should do

  • Do not swim, play, or fish in water that appears to have a cyanobacteria bloom.
  • Do not let your pets swim or play in water experiencing a cyanobacteria bloom.
  • If you or your pet comes into contact with waters experiencing a cyanobacteria bloom, wash with soap and water immediately.

What we are doing

The Rhode Island Department of Health and the Rhode Island Department of Environmental Management work cooperatively to monitor the state’s lakes and ponds to detect the presence of cyanobacteria blooms and to advise the public of health concerns. The Department of Environmental Management’s Office of Water Resources monitors lakes with reported blooms and lakes that have historically had high nutrient and/or chlorophyll a levels (factors that lead to blooms). The agencies jointly issue Health Advisories when any of the following three criteria, which indicate that a bloom exists, are met:

  • Evidence of a visible cyanobacteria scum or mat.
  • Cyanobacteria cell count exceeding 70,000 cells/mL.
  • Toxin (Microcystin-LR) level of lysed cells meeting or exceeding 14 ppb (ug/l).

Health advisories remain in effect for the remainder of the swimming season, unless follow-up sampling by a city, town, or third party indicate that the advisory can be lifted. Health Advisories may be lifted after two successive and representative sampling rounds, two weeks apart, demonstrate no evidence of an algal scum or mat and demonstrate cyanobacteria cell counts and toxin levels below threshold concentrations.

Bodies of water with cyanobacteria in the past

Body of water City or town Year(s) Dominant cyanobacteria species
Melville Pond Portsmouth 2010 Anabaena, Microcystis
Almy Pond Newport 2010 Aphanizomenon, Microcystis, Anabaena
Central Pond East Providence 2010, 2007 Microcystis
Turner Reservoir East Providence 2010, 2007 Microcystis
Lower Ten Mile River East Providence 2007 Microcystis
Omega Pond East Providence 2007 Microcystis
Mashapaug Pond Providence 2001 N/A
Yawgoo Pond South Kingstown 1998 N/A