It’s actually 950 acres, according to current information. This is mid- to late-60s.
Tennessee acquired the land for the park in 1952. Fort Patrick Henry Lake was fully impounded in 1953.
Looking over old maps of this area, I found that Duck Island didn’t exist, as an island, before the impounding of the lake. It was just the eastern shore of the South Fork of the Holston River above Wexler Bend. And somewhere in there, it got ducks.