Mountain Island is an unincorporated community in eastern Gaston County, North Carolina, United States.

Located on the extreme southwestern end of the lake, the island is mainly used as an anchor point for recreation, picnicking, and camping.

A cotton mill, said by some authorities to be the first in Gaston County, was established on Mountain Island in 1848 by Thomas R. Tate and Henry Humphreys, owners of the Mount Hecla steam-powered mill near Greensboro, North Carolina.

The site at river's edge featured a partially completed canal around the shoals that could be used for a mill race, and a steep island whose top now rises from the lake.

Machinery was moved from the Mount Hecla mill by mule-drawn wagon and operations began in 1849.