Water quality was monitored in the Willamette and Columbia Rivers during a pilot dredging operation on December 16, 1977. Monitoring included in-situ measurements of pH, temperature, dissolved oxygen, and conductivity in the Willamette and Columbia Rivers; analyses of dissolved ammonia, dissolved manganese, suspended-sediment concentration and particle size, loss on ignition, and total organic carbon in river-water samples; and analyses of percent moisture, particle size, density, selected nutrients, total organic carbon, and loss on ignition in dredged material and barge-overflow samples.