sentences:  In late spring (mid-May to mid-June), the Lochsa River is rated as one of the world's best for continuous whitewater.The main stem of the Lochsa is in length from its headwaters near Powell Ranger Station in the Bitterroots to Lowell, where the Lochsa joins the Selway River to form the Middle Fork of the Clearwater.Over this distance, the river drops nearly , from above sea level at Powell to at Lowell.