Bahia Honda (meaning deep bay, in Spanish, locally pronounced: BAY-ah HON-da [ˈbeɪə 'hɒndə], also pronounced (in Spanish): Bah-EE-ah OWN-dah [ba'ia 'onda]), is an island in the lower Florida Keys.

U.S. 1 (the Overseas Highway) crosses the key at approximately mile markers 36-38.5, between Ohio Key and Spanish Harbor Key 12 miles (19 km) west of Marathon, close to the west end of the Seven Mile Bridge.

The island is virtually uninhabited, being home to the 524-acre (2.12 km2) Bahia Honda State Park. Founded in 1961, the park occupies most of the island. The channel at the island's west end is one of the deepest natural channels in the Florida Keys.
Marine life is quite plentiful in the waters surrounding the island. Just off the beach snorkelers can spot many species of small reef fish, as well as rays, barracuda, and even the occasional small nurse shark.

The only known natural colony of the now rare Miami blue butterfly was discovered in the park in 1999. The butterfly had been thought to have become extinct as a result of Hurricane Andrew in 1992.

The 2.5-mile (4.0 km) natural, white sand beach was rated the #1 beach in 1992 in the United States by "Dr. Beach" Stephen Leatherman (the first Florida beach to be so honored), making it popular for swimming. A nature trail near the park’s oceanside beach skirts a tidal lagoon before passing through a coastal hardwood hammock. Bicycling and inline skating can be done on the park’s 3.5-mile (5.6 km) paved road, and there are several fishing and picnicking spots in the area. The Sand and Sea Nature Center features displays about local sea and shore life, including corals, shells, crabs, sea urchins, drift seeds, sea sponges and sea turtles.

Kayaks and snorkeling gear can be rented at the park, and boat trips for snorkeling on the reef are available. The park has a marina with boat slips available for overnight rental. Campsites (primitive and full hook-up) and vacation cabins are available, although reservations for the winter months can be very difficult to get.

The park is also a part of the Great Florida Birding Trail.