Nestled in a forested valley on the west flanks of Mt. Jefferson, the Metolius is one of the largest spring-fed rivers in the United States. The Metolius River originates from springs that rise from the base of Black Butte, a composite volcano that rises over 3400 feet above the river. The river flows north for 18 miles and then bends east for another 10 miles around the  north end of Green Ridge, eventually flowing into the reservoir Lake Billy Chinook. Many spring-fed streams are tributary to the Metolius River and contribute to the high water quality that is characteristic of the watershed. The river has relatively high velocities and little overhead cover except that provided by deep water pools.

The upper Metolius River flows through a basin influenced by glaciation and volcanism. The tributaries flow east off the slope of the Cascade Mountains and traverse zones of lava flows, glacial moraines and outwash sand and fine gravels. The Metolius Basin is a depression identified as a garben, formed by a central block slipping down between Green Ridge and the Cascades.

The hydrograph of the Metolius River is quite stable due to the spring-fed nature of many of the tributaries of the upper basin. High precipitation events occur as rain-on-snow events in late fall or early spring, as well as high intensity thunderstorms in August. The Cache Creek drainage discharges storm runoff into Lake Creek, just above its mouth at the Metolius River. Cache, First and Canyon Creeks have an important influence on the hydrograph of the Metolius and discharge relatively significant sediment loads compared to other Upper Metolius Basin tributaries.

The lower river, adjacent to the Warm Springs Indian Reservation, is managed as a primitive area with no motorized access.

Bull trout, redband trout, kokanee salmon, and mountain whitefish are native to the Metolius River Basin. Chinook and sockeye salmon were indigenous to the basin, but are no longer present. Other fish available for recreational angling include naturalized populations of introduced brook and brown trout, and hatchery releases of rainbow and cutthroat trout.