-The White River of Arkansas and Missouri formerly supported a numerous and diverse assemblage of freshwater Mollusca. Reservoir construction, channelization, and other methods of stream regulation have altered the basin extensively. Of the approximately 100 species once knwn from the White River system, 64 species have been collected during recent sampling from the primary channel of the river. The remainder of the molluscan fauna appears to have been extirpated from the main channel. Isolated populations of these species may still occur in some of the tributaries. The decline of the freshwater molluscan populations, particularly mussels, became a major concern shortly after the beginning of the 20th century. The cause and interest at that time were both generated by the use of the shells in the manufacturing of buttons and, to a lesser extent, the collecting of pearls (Coker, 1919). This resulted in some of the major studies conducted on the freshwater fauna of the United States (e.g., Lefevre and Curtis, 1912; Meek and Clark, 1912; Wilson and Clark, 1914; Coker et al., 1921). The concern was again voiced by Ortmann (1924) over the damming of Mussel Shoals. Today, primary threats to the American fauna are derived from pollution, stream alteration, and the effects related to the encroachment by Corbicula, although a commercial market for shells has again developed due to the Japanese cultured pearl industry (Van der Schalie, 1969). This paper presents a preliminary overview of the alteration to the White River in Arkansas and Missouri and the resultant effects on the molluscan assemblages. STUDY AREA.-The White River is approximately 1,210 km long with a drainage basin of 72,520 km2 (Fig. 1). It originates on the northern slope of the Boston Mountains, the southernmost of the Ozark Plateaus, in northwestern Arkansas and flows northeasterly into south-central Missouri. It then follows a southeasterly route back into Arkansas and leaves the Ozarks near Batesville, Arkansas, a short distance upstream from the confluence of the Black River. The last 420 km of the river are a lowland stream in the Mississipi Alluvial Valley. This channel represents a former course of the Mississippi River (Gordon et al., 1980). Improvement of the White River for navigation was begun in 1871 by the Army Corps of Engineers. Projects were authorized by the River and Harbor Act of 1892 for development from the mouth to Forsyth, Missouri. A series of locks and dams above Batesville were authorized in 1899, but never completed. The effective head of navigation became Batesville (river km 484). The navigation channel is now maintained from Newport, Arkansas (river km 418), to the mouth at an annual coast of about $1,000,000. It is navigable about 75% of the year. A recent proposal to deepen and widen the channel has been abandoned due to prohibitive costs (US Army, 1965; Griffee, 1980). The Ozark portion of the river has been dammed five times between river km 675 and 1125. These were built from the late-1940's througth the mid-1960's and include four Army Corps of Engineers projects and a small municipal facility. These are, in an upstream progression, Bull Shoals, Taneycomo, Table Rock, and Beaver reservoirs, which all utilize hypolimnetic release, and the city of Fayetteville's Lake Sequoyah. The headwaters of the White River lie above Lake Sequoyah. This area has been moderately affected by pollution and some gravel removal. The This content downloaded from 157.55.39.163 on Wed, 21 Sep 2016 05:37:22 UTC All use subject to http://about.jstor.org/terms The Southwestern Naturalist