Montgomery Parks urges patrons to use caution when recreating on or near Lake Needwood and Lake Frank located within Rock Creek Regional Park due to potential risks associated with high levels of blue-green algae (cyanobacteria). Water samples from both lakes are currently being evaluated by the Maryland Department of the Environment (MDE) to determine if levels are harmful. Visual indicators including discolored water and algal mats have been observed in portions of both lakes. Harmful Algal Blooms (HABs) can produce dangerous levels of toxic microcystin.