Peltigera gowardii, or western waterfan, is an aquatic lichen found only in mountain streams of Western North America. It is the largest aquatic lichen in the Pacific Northwest. P. gowardii is currently listed as a species of Special Concern in Canada, as two of five known populations have been extirpated. In the United States, Montana and Alaska list this lichen as an , at high risk of extirpation, while Washington and California give it a slightly more secure ranking. Rising temperatures and habitat loss are the largest threat to the survival of P. gowardii.