"PB2000-107420."Water quality changes along hyporheic flow paths may have important effects on river water quality and aquatic habitat. Previous studies on the Williamette River, Oregon, showed that river water follows hyporheic flow paths through highly porous deposits created by river channel meandering. To determine water quality changes associated with hyporheic flow, we studied six bar deposits positioned between the river and closed lentic side-channel alcoves. At each site we measured water levels and water quality in river, hyporheic, and alcove water. At all sites we found hyporheic flow paths from the river through the bar deposits to the alcove surface water. At a majority of the sites hyporheic dissolved oxygen and ammonium decreased relative to river water, while hyporheic specific flow rates, hyporheic temperature decreased relative to river water, and there was little change in temperature at the other three sites. Hypoheic changes most affected receiving alcove water quality at sites with fast hyporheic flow rates. Strategies to promote ecosystem functions provided by hyporheic flow should focus on restoring natural hydrogeophmorphic river channel processes to create high porosity deposits conducive to hyporheic flow.