The Wood River's largest tributary is Annie Creek which originates inside the boundary of Crater Lake National Park, and is fed by the park's snowpack as well as groundwater from natural springs. After leaving the park, Annie Creek passes through the Fremont-Winema National Forests and then runs along the western border of Sun Pass State Forest for about a mile. It then crosses private pastureland and is joined by Sun Creek before joining the Wood River, about a mile south of Kimball State Recreation Site.