For decades environmentalists have been advocating for a swimmable and fishable Charles River, and this spring one critter gave its seal of approval. In April, a seal was spotted swimming near the BU Bridge; later that month, a seal was found further downstream near the Charles River Dam before being coaxed back into the Boston Harbor. The experts at the New England Aquarium soon weighed in, saying the crafty seal was likely trying to find some easy food in the freshwater of the Charles. Let’s just hope the sharks don’t follow.