In the summer of 2016, a population of Lepomis peltastes (Northern Sunfish), a New York State threatened species, was discovered in an 8-km reach of the Great Chazy River in Clinton County, NY. This population is the first known from the Lake Champlain watershed. Further investigation showed the population extending upstream of the lowest fish barrier for 2.3 km. Northern Sunfish were found in sheltered habitat shared with several other species of Centrarchidae. While a variety of methods were successfully used to catch Northern Sunfish, backpack electroshockers were the most effective. The future of the Northern Sunfish in New York is discussed, as well as the ecological implications for some of the other fish species in the river.