They are frequently found patrolling the edges of the stream, cruising in and out of underwater rock crevices in search of crawdads and small fish, or anything else they can get their mouths around. Wikipedia says they can also project themselves out of the water, up to 2 m in height to attack prey such as small birds and insects.
Like many snakes, they will bite if threatened and release excrement and musk as a further deterrent. Their saliva contains a mild anticoagulant, which can cause the bite to bleed more but poses little risk to humans.
Our friend pictured here was found by our neighbor Larry Whiteley. It was just starting to devour a perch head first. By the time we went back for a camera it was almost done, with just the tail protruding from its mouth. With its jaw displaced for swallowing, the head had an ominous triangular shape but the pupil was round, not to be confused with a venomous water moccasin.
|Copperhead out for a swim|
A good resource for the Snakes of Missouri is on this Missouri Department of Conservation web page.