Nerodia is one of my favorite snakes and I catch and release about a dozen of them a year. This is an excellent native herp to keep because they are so abundant in most states, and often the easiest snake to find since they stay near water while most terrestrial snakes are nomads (I saw 25 last year vs. only 8 blacksnakes). Their aggression disappears with simple handling in a matter of weeks. In my state a permit allows you to keep up to 2 of any non-endangered species so you can breed as many as you want, however no one I know has ever actually been asked to have a permit. If you want to keep more I'd recommend doing volunteer nature programs, which allows you to hand-pick them for particular markings and disposition. Rescuing them from roads and brutal citizens is a good cause, although theyre pretty inexpensive in the pet trade albeit not too common.
Experience has taught me to use a terrestrial tank with a large basin rather than an aquatic tank with a large island, because soiled water (even if it looks clean) accelerates the effects of a dirty tank on the snake's skin. Do not use cedar bedding. My faithful idiots in the nature lodge filled the tank with cedar last year and the snake got an eye infection from burying in it. I feed mine 3 to 5 frogs or toads per week in summer, and 5 to 8 large goldfish or minnows in winter. I dont feed them all at once to avoid fighting and overeating. They are easy to breed since they birth live (mine had 36 babies in august).
Females are usually twice the size of males. They can be kept with garters, ribbons, blacksnakes and most other species from the same area. Do not mix wild and captive-born snakes. Skin problems clear up with shedding and a change of living space. There are so many colors, patterns and phases in this genus Ive never read a guide that did them justice.
Len