Denver park officials say it could be another three to four weeks before Ferril Lake at Denver's City Park is back to normal.
Right now, the lake is covered in green algae.
Staff say the algae typically forms during hot weather and could get worse if the weather gets any warmer.
Crews were out on Wednesday skimming the surface of the lake. They’re also using vacuums to suck up the algae.
Scott Gilmore, Deputy Exec. Dir. for Denver Parks and Planning, says the algae is not toxic or dangerous to touch.
He says the algae forms on several lakes around the city every year during the summer.