RIDOH and DEM Lift Advisory at Lake Tiogue and Oak Swamp Reservoir

What this means

The Rhode Island Department of Health (RIDOH) and Rhode Island Department of Environmental Management (DEM) have lifted the recommendation to avoid recreational activities at Lake Tiogue in Coventry and Oak Swamp Reservoir in Johnston. The harmful algae bloom (HAB) caused by blue-green algae (cyanobacteria) has cleared. Recent water testing laboratory results show algae levels are low and no toxins were detected, meeting safety guidelines.

Official release

Source material from Rhode Island Department of Environmental Management — Agriculture. The wording below is the issuer’s statement.

RIDOH and DEM Lift Advisory at Lake Tiogue and Oak Swamp Reservoir

Published on Friday, September 18, 2026

The Rhode Island Department of Health (RIDOH) and Rhode Island Department of Environmental Management (DEM) have lifted the recommendation to avoid recreational activities at Lake Tiogue in Coventry and Oak Swamp Reservoir in Johnston. The harmful algae bloom (HAB) caused by blue-green algae (cyanobacteria) has cleared. Recent water testing laboratory results show algae levels are low and no toxins were detected, meeting safety guidelines.

HAB conditions can change quickly. Water with HABs may exhibit bright to dark green scum along the shoreline with thick, floating algal mats on the surface. The water may resemble green paint, pea soup, or green cottage cheese. If you see water in this condition, keep people and pets away from it. Toxins may persist in the water after a blue-green algae bloom is no longer visible.

To report suspected blue-green algae blooms, contact DEM’s Office of Water Resources at DEM.OWRCyano@dem.ri.gov or call 401-222-4700, Press 3, and select Office of Water Resources. If possible, send a photograph of the reported algae bloom. For more information and the Cyanobacteria Tracker Dashboard that lists current advisories and data, visit: www.dem.ri.gov/bluegreen

Date

Fri, 09/18/2026 - 16:16

Release text attributed to Rhode Island Department of Environmental Management — Agriculture. Consult the official publication for any subsequent corrections or updates.