DERWOOD, Md. (WDVM) — Officials are warning residents of possible toxic algae in portions of two Montgomery County lakes.

If you’re planning any activities near Rock Creek Regional Park, pay close attention to your pets as there are signs of higher levels of microcystin at both Lake Needwood and Lake Frank. Since 2009, Montgomery Parks have been testing the water for blue-green algae which is toxic for pets and humans when consumed – causing liver damage. Signs are posted around lakes and trails, warning visitors not to swim and to be sure dogs are on a leash.

Park officials are also suggesting to avoid direct contact with water while boating or fishing, at this time, as parts of the lake could be contaminated for the rest of the season. Natural Resource Manager at the Department of Parks M-NCPPC, Montgomery County, Matt Harper said, “Based on what we observed in the lake, and what we’ve seen in previous years, we decided to go ahead and post signs that indicate there is a risk.”

Recreational activities, including boating and fishing, will remain open at the lake. If you make contact with the water, make sure to wash your hands thoroughly. If fishing, be sure to properly cook any fish you catch before eating them.