Potentially toxic algae blooms have been found in northeastern Colorado reservoirs, Colorado Parks and Wildlife announced in a press release.

On Friday, the department announced that toxin levels are being tested at North Sterling State Park, Jackson Lake State Wildlife Area, Prewitt State Wildlife Area and Jumbo (Julesburg) State Wildlife Area.

CPW inspects bodies of water weekly for signs of harmful algae, especially during the summer months. When algae is found, the Colorado Department of Public Health and Environment tests cyanobacteria samples for microcystin, an algal toxin.

CDPHE says 8 micrograms per liter (ug/L) of algal toxin (microcystin) and above is considered “red” level. Anything below 8 ug/L is considered “yellow” level. 

Samples collected from North Sterling reservoir on July 17 showed microcystin concentrations of 7.3 ug/L at the swim beach and 4.6 ug/L at the marina, causing the swim beach to be shut down, according to the press release.

Jumbo SWA samples had low concentrations of toxins and tests on Prewitt SWA and Jackson Lake SWA are still pending.

The North Sterling swim beach was first closed last week. Swimming, paddle boarding and wade fishing are not permitted. 

“It’s especially important to keep dogs on a leash by the swim beach, so they aren’t tempted to drink from the water while we’re experiencing an algae bloom,” North Sterling Park Manager David Piper said in the report.

While Prewitt, Jumbo and Jackson Lake State Wildlife Areas have yet to be officially deemed “red level,” CPW suggests visitors wash off after touching the water and barring pets from the water in general.