Has anyone ventured a species identification for these snakes? Their triangular heads appear suspiciously like a viper such as the water moccasin or cottonmouth, which are venomous - although Maryland is pretty far north for either of these to be found. However, the common water snake can also look quite forboding. My understanding of snakes is that they are not voracious - i.e., they don't eat a lot - and unless there is an absolute infestation of them, they do not threaten to decimate wildlife numbers. Their primary source of food in the wild is rodents, which is a good thing. Here in central Florida, I am happy to find black snakes and green snakes around my ponds. They are anything but aggressive.
