Distinctive stocky waterbird. Adult is dark gray overall with a white bill and forehead shield. Immature has a pale breast and a duller bill that becomes brighter white with age. When walking on shore, note big feet with lobed toes. Inhabits both freshwater and brackish marshes, lakeshores, and riverways; occasionally on saltwater. Breeding pairs aggressively territorial but nonbreeding flocks can number in hundreds. Unmistakable throughout much of range, but compare with very similar Red-knobbed Coot in areas of overlap. Calls are diverse, and include various high-pitched squeaks, squawks, and shorter, more clipped notes.