The most southern of the three Kama'ole Beaches, Kama'ole III is my personal favorite.
The swimming is fair, not spectacular. There is a lifeguard. For the best swimming, I suggest Kama'ole I. There are some snorkeling opportunities around the rocks at the beach's south end. You'll see quite a few boogie boarders and bodysurfers at Kama'ole III.
The real attraction, though, is the beach park itself. It features an exceptionally wide, grassy area. It's one of the most popular places on Maui for family gatherings and picnics.
There is plenty of off street parking, barbecue grills, restrooms, showers and water fountains. There is a nice playground area for children.