BOSTON. Scientists who tested water samples in the Muddy River this week found blue-green algae at potentially harmful levels in the Fens area, according to the Charles River Watershed Association.

Health officials say residents and animals should avoid contact with the algae for at least a couple of weeks and potentially throughout the rest of the summer. The agency reported the algae is an aquatic, photosynthetic bacteria that has long been found in freshwater bodies in Eastern Massachusetts, but its growth recently has increased the potential health risks.