Complex sentence: They appear in most of the inland waters of the United States: the South Carolina coast, the Gulf coast adjacent to the Florida panhandle, and the Atlantic seaboard from Massachusetts to Maine have some of the highest concentrations of common loons.
Split into simpler sentences: They appear in most of the inland waters of the United States. The South Carolina coast, the Gulf coast adjacent to the Florida panhandle, and the Atlantic seaboard from Massachusetts to Maine have some of the highest concentrations of common loons.