The notorious toxic algae that killed dogs across the country and closed three bodies of water in the Pikes Peak region last summer has likely made a comeback at Prospect Lake in Colorado Springs, city officials cautioned Monday.

The lake at Memorial Park is closed until further notice because of a “presumed” return of blue-green algae, according to a news release.

A Colorado Springs Utilities crew is to test a water sample from the lake Tuesday to confirm the presence of mycrocystin toxin, which is produced by cyanobacteria, also known as the blue-green algae.

“Given (Monday’s) visual inspection, and the lake’s recent history with mycrocystin toxin, we have closed Prospect Lake for usage at this time. If Tuesday’s water sample returns positive, we will continue to test weekly until the bacteria clears up,” said Erik Rodriguez, health, safety and environmental specialist with the city’s Parks, Recreation and Cultural Services Department.

Prospect Lake was closed for 12 weeks in 2019 during late summer and early because of blue-green algae.

Colorado Springs’ staff has since applied an enzyme-based, non-pesticide treatment that consumes biomass at the bottom of the lake to help oxygenate the water. Algae blooms can cut off oxygen in the water. Treatments were applied May 26 and June 11, and the next treatment is scheduled for Tuesday. Staff will add more water to the lake, which will also increase the oxygen level to dilute the toxin.

The bacteria harms water quality, decreases the amount of oxygen available to animals living in the water, and can be toxic to humans and pets.