Crab Creek is sometimes separated into Upper Crab Creek, which runs from the creek's source to
Potholes Reservoir, and Lower Crab Creek, which runs from Potholes Reservoir to the Columbia River. Sometimes the stream is divided into three parts—Upper Crab Creek, from its source to Brook Lake, Middle Crab Creek, from Brook Lake to and including Potholes Reservoir; and Lower Crab Creek, from below Potholes Reservoir to the Columbia River. Upper Crab Creek was dry before the CBP and remains intermittent today. From its source near Reardan it flows generally southwest then west, collecting tributaries including Rock Creek, Coal Creek, Duck Creek, Canniwai Creek, and Wilson Creek. It empties into Brook Lake, located just south of
Billy Clapp Lake, an
equalizing reservoir of the CBP created by
Pinto Dam. Crab Creek turns southward after Brook Lake. The CBP's East Low Canal, one of the projects main irrigation canals, crosses but does not mix waters with Crab Creek. At the city of
Moses Lake Crab Creek empties into the Parker Horn arm of
Moses Lake. Just before reaching the lake Crab Creek receives the waters of Rocky Coulee Wasteway, a mix of the intermittent Rocky Coulee Creek and irrigation runoff from the East Low Canal. Before the CBP there was no perennial flow between Brook Lake and Moses Lake. Only during periods of high water did Crab Creek flow through this area. Moses Lake empties into Potholes Reservoir, which feeds irrigation canals to the south. Below O'Sullivan Dam several springs renew Crab Creek, which flows southwest, then west. Below the community of Smyrna, Crab Creek meanders across a two mile-wide canyon, bounded on the south by
Saddle Mountains and on the north by the Royal Slope and containing portions of the
Columbia National Wildlife Refuge, before emptying into the Columbia River. ==Lakes==