Just after the state warned about cyanobacteria bloom in the Charles River, the city has closed Crystal Lake for the same issue.

Newton officials announced on Wednesday that cyanobacteria (commonly called blue-green algae) blooms in the lake were big enough to pose a danger.

“In consultation with the Massachusetts Department of Public Health (MDPH), Newton Health and Human Services (HHS) determined that all of Crystal Lake must be closed at this time because of potential health risks,” Mayor Ruthanne Fuller wrote in an email to residents Wednesday.

Cyanobacteria often grows in freshwater ponds, lakes and rivers during hot periods with little rain, when water is stagnant. When blooms get big enough, the water becomes toxic. And pets are especially vulnerable.

“No one—humans or pets—should have contact with the water,” the mayor cautioned.

Don’t swim in the lake, don’t drink the water or let your pets drink it, don’t bring boats onto the lake, avoid contact with the water, keep pets away from it, and if you or your pets have come into contact with the water, rinse off immediately.

If you or your pets develop nausea, diarrhea or a fever after being near the lake, you should seek medical attention immediately.

The state has more information on cyanobacteria.

Crystal Lake will stay closed while officials monitor the safety of the water. Meanwhile, Gath Pool is honoring Crystal Lake season passes for the rest of the season.