While walking along the shore of Big Bend Lake in Des Plaines, Illinois I heard some rustling in reeds and the cause of that commotion was two northern water snakes.
While not poisonous, these snakes can inflict a painful bite. The saliva of these serpents contains a mild anticoagulant--the bites can be bloody. But American snakes are like bees--you don't bother them and they won't bother you.
Four Corners Furtherance: My rattlesnake sighting