The lower Crooked River defines Crook County.  The river meanders north from Prineville Reservoir, flows through Prineville, and continues past scenic Smith Rock State Park to Lake Billy Chinook.   Dams and diversions along this reach have provided for recreation and agriculture, but they have also eliminated anadromous fish and impaired riverine ecosystems.

Streamflow in the lower Crooked River varies by season and by location on the river.  Streamflow below Prineville Reservoir is highest during the summer and lowest during the winter, the opposite of natural conditions.  Streamflow downstream of the North Unit Irrigation District's pumps is low year-round.