There are a few trails that lead from the camping areas to the lake but they aren't really hiking trails. The only real hiking trail is the Mariah Mesa Trail. It leads up a slight rise to a mesa (a flat plateau) that offers some decent views of the lake and the area around the park. The trail is not very long and is fairly easy. There is also a short nature trail with numbers corresponding to a little booklet that identifies the plants you see.
Equipment: Good walking shoes, a hat, sunscreen, water, weather appropriate clothing.
I did not try the fishing myself; but I saw several people catching fish and the ones I talked to said the fishing is good here. You can fish from a boat, the shoreline, or a dock.