Great post Stan!
The black spot is a parasite which goes through different life stages starting with the fish and using snails and birds to produce successive generations. While they look bad, they are typically not too harmful to the fish and are not of concern to humans. It is a common parasite, but I'm sure you've noticed it is more prevalent in some places than others - likely because it prefers soft substrate bottoms which here in RI is most everywhere. They sure don't look appetizing and the fact that they are there means water fowl is there as you mentioned, which means fecal coliform is likely high. I know Slacks has tested high for that in the past.
