Cyanobacteria (Blue-Green Algae) Film on surface of water from blue-green algae can look like spilled paint Thick green foam may wash ashore during a bloom Blue-green algae may make the water look cloudy with a green tint Blue-green algae may make the water look like pea soup Prev Next Slide 1 Slide 2 Slide 3 Slide 4 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. 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 Past Advisories On 12/22/2023, the Rhode Island Department of Health (RIDOH) and the Rhode Island Department of Environmental Management (DEM) lifted the recreational advisories at Waterman Reservoir in Glocester/Greenville, Little Pond in Warwick, Blackamore Pond in Cranston, and Indian Lake in South Kingstown. Almy Pond in Newport, Roger Williams Park Ponds in Providence, J.L. Curran Upper Reservoir, Spectacle Pond, and Mashapaug Pond in Cranston remain under advisory due to continued visual evidence of blue-green algae. Blue-green algae are generally less active as seasonal changes reduce light and temperature in the winter. However, the possibility of recurring blooms and/or toxins represents potential risks, even in iced-over conditions. Sampling is over for the 2023 season however, we encourage people to report suspected blooms. Cyanobacteria Monitoring Program Reports Cyanobacteria Monitoring Program 2023 Report PDF file, about 4mbmegabytes Cyanobacteria Monitoring Program 2022 Report PDF file, about 3mbmegabytes Cyanobacteria Monitoring Program 2021 Report PDF file, about 3mbmegabytes Cyanobacteria Monitoring Program 2011 Report PDF file, about 3mbmegabytes Cyanobacteria Monitoring Program 2012 Report PDF file, about 3mbmegabytes Cyanobacteria Monitoring Program 2013 Report PDF file, about 5mbmegabytes Cyanobacteria Monitoring Program 2017 Report PDF file, about 2mbmegabytes Cyanobacteria Monitoring Program 2018 Report PDF file, about 1mbmegabytes Cyanobacteria Monitoring Program 2019 Report PDF file, less than 1mbmegabytes Cyanobacteria Monitoring Program 2020 Report PDF file, about 6mbmegabytes Resources Cyanobacteria (Blue-green Algae) Factsheet PDF file, about 2mbmegabytes Controlling Algae in Your Pond PDF file, about 1mbmegabytes Five Reasons Why Feeding Waterfowl is Harmful PDF file, less than 1mbmegabytes Ten Things You Can Do to Improve Water Quality in RI PDF file, less than 1mbmegabytes Eutrophic Ponds Approved TMDL PDF file, about 4mbmegabytes Septic System Checkup Manual PDF file, less than 1mbmegabytes 2020 Rhode Island HAB Cyano Coordination Meeting Presentation PDF file, about 5mbmegabytes 2012 RI Lakes Report PDF file, about 11mbmegabytes 2017-2018 Harmful Algal Bloom Monitoring QAPP PDF file, about 2mbmegabytes Cyanobacteria Harmful Algal Bloom ID and Enumeration PDF file, less than 1mbmegabytes Select Cynobacterial Toxins By Direct Aqueous Injection PDF file, about 1mbmegabytes Cyanobacteria Fact Sheet and List of Advisories 2010-present PDF file, less than 1mbmegabytes 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