BIODIVERSITY of OUACHITA UPLAND RIVERS
Little River
The Little River, a major tributary of the Red River, drains 5,700 km2 in southeastern Oklahoma and southwestern Arkansas. The river is 349 km in length. The upper reaches of the river flow through the Ouachita Mountains and the upper watershed is heavily forested and used primarily for silviculture. Lower reaches of the river flow through the fertile bottomlands of the Gulf Coastal Plain. The Little River headwaters are boulder-cobble and gravel with well-developed pools and swift rapids until the mainstem forms Pine Creek Reservoir. Below the reservoir the river retains pool-riffle structure over a mostly gravel bed, with water willow a common structural feature in the shallows.

The Little River is influenced by two impoundments. The mainstem Little River is impounded by Pine Creek Reservoir, used for flood control, water supply and recreation. Approximately 30 miles below Pine Creek Reservoir, a sixteen mile section of the river flows through the Little River National Wildlife Refuge (15,000 acres). The section of the Little River on the wildlife refuge contains very diverse and healthy mussel populations, including a population of the federally endangered Ouachita Rock Pocketbook Mussel, Arkansia wheeleri. 64 km below downstream of Pine Creek dam, the Mountain Fork River enters the Little River. The lower Mountain Fork River is impounded by Broken Bow Reservoir which is used for hydroelectric power among other uses. Water entering the Little River from the Mountain Fork River is very cold, and mussel populations have been extirpated for many km downstream.