Crystal Lake is now safe again, after being closed for two weeks due to a cyanobacteria bloom. City officials say the danger has cleared and the water is safe again, Mayor Fuller announced in an email to the community Thursday.

Newton Health and Human Services and the Massachusetts Department of Public Health have collected water samples for testing twice since the closure, spacing the tests apart by a week.

“Two tests are required because cyanobacteria cells can release cyanotoxins into the water when they die. In other words, algal toxins may be present when a visible scum or mat is no longer evident,” Fuller explained.

Cyanobacteria potency is measured by cells per milliliter of water. Crystal Lake’s level on Aug. 19 (when the second sample was taken) was 12,000 cells per milliliter, way below the state’s 70,000 cells per milliliter limit.

“While the City of Newton Parks, Recreation and Culture swimming program with lifeguards and access to the bathhouse has concluded for the season, visitors are free to resume recreational enjoyment of the lake and surrounding park spaces,” the mayor wrote.

Commonly referred to as blue-green algae, cyanobacteria is common in rivers, lakes and ponds during the dry season and can release toxins that can cause skin rashes and respiratory issues, which are especially pronounced in children and pets.

Just a couple of days before the cyanobacteria bloom was found in Crystal Lake, and even bigger one was spotted in the Charles River.