Mound Key Archaeological State Park is a Florida State Park, located in Estero Bay, near the mouth of the Estero River. One hundred and thirteen of the island's one hundred and twenty-five acres are managed by the park system. It is a complex of mounds and accumulated shell, fish bone, and pottery middens that rises more than 30 feet above the waters of the bay.Mound Key was an important site of the Calusa tribe, and most experts believe it to be the site of their capital, Calos.