Lakes are good, too. A kayak can get in a lot of places that a boat couldn't. If you enjoy watching animals and birds, you can't beat a lake.
A river is the best, though. A deeper river flow is actually easier then a shallower flow. The rapids are much rougher when the water level is down. Those dog leg curves will try to dump you over every time. My goal each year is to stay upright.

One of our group did almost drown last year. She got caught in a strainer, and couldn't get back up to the surface. The group that runs the race did have a person posted there, so she got pulled back up to safety.