Greer Spring, in the Mark Twain National Forest of south-central Missouri, is a major karst spring and the second largest in the Ozarks, with an average flow of about 360 cubic feet per second. Rising from a narrow chasm, it sends cold water through a steep gorge to the Eleven Point River, greatly increasing the river’s volume, supporting boating in dry months, and creating good trout habitat. Designated a National Natural Landmark in 1980, it is also noted for its secluded, largely undisturbed setting. The spring was named for Captain Samuel Greer, whose mill operations began there in 1859 and continued under changing ownership until 1922.