Though a small lake, Lake Mary is popular with local boaters because it's the biggest one nearby. During drought summers, it gets small and shallow, but in wet years there's room for all kinds of boats (including motor boats). Popular uses for the lake besides simply paddling around include fishing, camping and watching meteor showers.
There is a fee of $6 to park in the launch/picnic area. There is also developed camping nearby at Lake View and Pine Grove campgrounds. Expect crowds in the summer, given that it's one of the biggest bodies of water in 50 miles.