Shell Key Preserve, Nature reserve in Pinellas County, Florida, US.

Shell Key Preserve is a nature reserve on Florida's Gulf Coast made up of barrier islands, mangrove forests, and seagrass beds. The individual islands and habitats lie scattered across the water, forming a zone where land and sea overlap in a continuous and shifting pattern.

Shell Key began as a submerged shoal on the north side of Bunces Pass and emerged as a barrier island in the early 1960s, first named North Bunces Key. The island has since grown as offshore swash bars migrate onto its beach, and storm breaches have opened and then closed again. It now forms part of the 1,800-acre Shell Key Preserve in Pinellas County.

Shell Key is one of Florida's most important areas for shorebird nesting and wintering, and it also serves as a study site for these species. To balance birds and visitors, public use is limited to the northern and southern ends of the island, while a central conservation core is closed to the public.

Shell Key Preserve can be reached only by boat; no restroom facilities are provided on the island. The nearest boat ramps, trailer parking and restrooms are at Fort De Soto Park. Public use is limited to the northern and southern ends of the island, while the central core is closed to the public for conservation.

The islands shift constantly due to wind and waves, so the landscape can look noticeably different from one visit to the next. In 2015, moving sand closed off a channel near the northern tip of the main island, changing how boats could approach that part of the preserve.