The Florida Reef Tract is the third largest coral reef system in the world, extending 356km from Miami to the Dry Tortugas. It has over 6,000 species of plants and animals and was formed over 1.8 million years as sea levels fluctuated during ice ages. The reef is made up of three geological regions: the Key Largo Limestone, Miami Oolite, and fossilized coral. It contains diverse marine habitats including coral reefs, seagrass beds, and mangroves that are threatened by pollution, overfishing, climate change, and invasive species.