subs. (American).A snag: a fallen tree, rising and falling with the waves.
1847. ROBB, Streaks of Squatter Life, 106. Snags and SAWYERS, just thar, wur dreadful plenty.
1884. S. L. CLEMENS (Mark Twain), The Adventures of Huckleberry Finn, and Life on the Mississippi (1883), passim.