Yes they can be very aggressive, and I have been to that island where Mike row was, and I have collected those same snakes!!!, I even got in a small boat, drifted about 20 yards off shore, and watched the water snakes emerge from the rocks and crevices to swim out to where we were...then they would dive down and stay under water for about 3-5 minutes before coming up with a gobie in their mouth, "mud-fish"......then they would swim back to shore and climb up on the rocks to consume their meal!!! It was like I was watching national geographic except alot cooler!!!