Potamogeton hillii Morong has been considered as either a rare or endangered species in all states and provinces where it occurs. Currently it is under review by the United States Fish and Wildlife Service for possible listing under the Endangered Species Act of 1973. Prior to 1960 it was collected at 25 localities. Since 1970, 78 new localities have been discovered. Throughout its range this species is mostly found in regions of limestone bedrock. Presently it is most abundant in western New England and northern Michigan, and during 1982 was relocated in Connecticut and Ohio. Potamogeton hillii appears to be spreading in the limestone regions where it presently occurs. This taxon is found growing in clear, cold waters of small streams, ponds, and beaver ponds with muddy substrates. The abundant winter buds and fruits produced apparently guarantee the continued spread of this species. Potamogeton hillii should not be considered further for protection nationally, nor should it be so listed in the states where locally abundant.