Did it look like this snake?
If so, it's a garter snake which is a common name given to small, harmless, small to medium size snakes. They can be found from the sub Arctic Plains of Canada to Central America - one reason I am glad I live in the UK :-)
Garter snakes populate a variety of habitats - forests, fields, lawns and woodlands but almost always there will be water nearby, either a pond or pool etc. Because amphibians make up a large part of their diet.
Talking of diet, they will also eat almost any creature that they can overpower, so things like slugs, earthworms, crickets, leeches, toads and rodents (okay, I am warming to this snake).
If disturbed, a garter snake will typically hide it's head and flail it's tail, but it may strike too!
These snakes discharge a rather nasty, musky scented secretion, so typically these snakes will not harm you but they do smell pretty awful when scared.