The island's beaches are mostly narrow strips of sand along the eastern shore, sometimes held in place by a seawall. Water at the shore is shallow, and most areas have seagrass.
The view from the beaches of the turquoise water and barrier reef is spectacular, and at least when the offshore prevailing winds are blowing, which is most of the time, there are few mosquitoes or no-see-ums to bother you.
A number of hotels remove the seagrass from parts of their beach or from a swimming area at the end of their pier. While not the best move environmentally, this does make the swimming more pleasant.
No one beach stands out as being outstandingly better than others. Indeed, except in areas of mangroves, there is a continuous narrow thread all along the Caribbean shore. For those in and near town, the beach at Ramon's Village is one of the best for swimming. Another above-average beach south of town is at Mar de Tumbo near Villas at Banyan Bay and Tropica Hotel. North Ambergris Caye has long stretches of beach that is tropically beautiful though, again, not especially wonderful for swimming. Some of the beaches on North Ambergris got a new load of sand, thanks to Mitch.
Caution! Don't swim out too far from the beach or in areas heavily used by power boats. Several swimmers have been injured and even killed in accidents with boats.