At first, Jamaica Pond seems fine - you come down the slope from Perkins Street and there's a swan slowly moving across the water.
But then you walk over towards the Jamaicaway/Pond Street side and you see none of the sailboats have sails:
And you get to the boat-rental place:
And then you look down at the water along the shore and it's a murky shade of green.
So keep your pets and kids out of the water and don't go fishing for awhile.