LAUREL, Md. — A potentially harmful algae bloom has prompted warnings for people to stay out of a reservoir in Montgomery and Howard counties in Maryland.

The Washington Post reported Thursday that the body of water is the Triadelphia Reservoir.

The reservoir provides water to WSSC Water, which serves Montgomery and Prince George’s counties.

Drinking water is not affected, although the utility is testing for the algae at a water filtration plant. The bloom is of cyanobacteria, which is also known as blue-green algae.

It is common in stagnant water during warm weather and when there is higher levels of nutrients from runoff. The algae can cause a rash as well as gastrointestinal and respiratory problems.