Water snakes are not "aggressive." Something aggressive would chase and attack you. All a water snake will do is strike or bite if you try to catch or corner it. Otherwise, it will slither away. It is basically harmless.
There are no water moccasins (which are poisonous) in MA. There was the deadly Chappaquiddick Water Snake (a.k.a. Great Bloated Swimmer), which drives its victims into the water and drowns them, but the last known individual died a few years ago.
I will tell you a story told to me by my limnology professor in graduate school. He loved to drink warm beer from the trunk of his car while he fished in the Sabine River near Orange, Texas. He was a great professor and a drunk and fishing was his passion. Often he would make friends with other fishermen. One night a very rotund man, tipping the scale at about 325, was running a trotline (fishing for catfish) He would awaken about every 2 hours to run his lines. And....he was deathly afraid of snakes. He would lay on a sleeping bag on the banks of the Sabine, and he and my professor would talk (My teacher used a rod and reel). But come 12 midnight the fat fellow would get sleepy and try to get some shut-eye. I don't remember is he had a windup clock to awaken him, but as he was arousing about 2 a.m. he felt something of his neck and face. He sat up and as he tried to gain his sensibilities a large 6 foot diamond-back water snake (Genus Natrix) grabbed him on his rosey cheek. Now the Natrix is not poisonous, but he has a row of substantial retroflexed upper and lower teeth, which grabbed very hard. As our fatman literally pulled the snake from his attachment to his face and 'flung' (yes, down here in Texas we do say flung... and we mean it). The terrified fellow screamed a cottonmouth had gotten in the face and he was going to die. He was at least 45 minutes to an hour to a hospital. He said he was screaming the entire way. He was not envenomated, but did get a serious infection.
I have seen these large Natrix eat other snakes, even other Natrix, as long ast they are.
Natrix is not aggressive, but the Cottonmouth watermouth is very agressive. Large ones can be very dangerous.