The variability in the quantity and quality of surface irrigation return flows from two representative California irrigation projects are reported. The two projects are: (1)The 66,420 ha Glenn-Colusa Irrigation District in the Sacramento Valley, and (2)the 17,820 ha Panoche Drainage District for 1975, a typical irrigation season. The variations noted are attributed to differences in water application methods, crops, soil chemical and physical properties. The impacts of return flows to the Sacramento and San Joaquin Rivers are appraised and examined relative to the ongoing Section 208 Water Quality Management Planning efforts.