Not to humans, no. All members of the genus Nerodia, which include Banded Water Snakes (Nerodia fasciata) have enlarged, grooved rear teeth and a mild venom (NO snake is "poisonous", actually) secreted by Duvernoy's glands, which are modified saliva glands. Ditto for their close relatives, the Garter and Ribbon Snakes. The venom contains a mild anticoagulant which briefly inhibits blood from clotting, resulting in free blood flow for a few seconds. This is not dangerous to humans unless you have a pre-existing condition, such as Hemophilia, which already causes blood clotting issues, in which any little nick or break to the skin can be serious. I breed several species of Nerodia, by the way, and they actually tame down very quickly and make excellent pet snakes, especially if you're squeamish about feeding rodents to a snake, since they eat fish. They are no more "ill-tempered" than a Corn Snake or other popular pet snake species. My avatar, in fact, is a hypomelanistic Banded Water Snake.
