The Meramec River is one of the longest free-flowing waterways in Missouri, draining 3980mi2 while wandering from headwaters near Salem to where it empties into the Mississippi River near St. Louis at Arnold and Oakville. The Meramec watershed covers six Missouri Ozark Highland counties—Dent, Phelps, Crawford, Franklin, Jefferson, and St. Louis—and portions of eight others—Maries, Gasconade, Iron, Washington, Reynolds, St. Francois, Ste. Genevieve, and Texas. Between its source and its mouth, it falls. Year-round navigability begins above Maramec Spring, just south of St. James. The Meramec's size increases at the confluence of the Dry Fork, and its navigability continues until the river enters the Mississippi at Arnold, Missouri.
