The South Water Caye Marine Reserve covers a large area of the barrier reef about 20 km east of Hopkins — much closer and more accessible than Glover's Reef. The snorkeling is excellent: healthy coral heads, clear water, and an unusually good chance of seeing manatees in the grass beds near the cayes. West Snake Caye and the waters around Blue Ground Range are particularly worth visiting.
Several Hopkins operators offer half-day and full-day snorkel trips out here. Prices are lower than comparable trips on Ambergris Caye or Caye Caulker, partly because Hopkins attracts fewer tourists and partly because the boats don't have to go as far. The reserve is also good for fishing — bonefish flats inside the reef draw fly fishers from North America, though most of the local guides work on a catch-and-release basis. If you see a manatee, keep your distance and don't chase it; they surface to breathe and get spooked easily.