The flux of NO^-₃ and BOD values in the Yamato river water directly increased with precipitation. Therefore, the NO^-₃ was considered to originate mainly from fertilizer (A) because it was reported that the flux of NO^-₃in farmland drainage increased with precipitation, although domestic sewage (B) also contains a lot of NO^-₃. As sediments in the river channels and drains containing organic compounds migrated on rainy days, river BOD values are considered to increase after rain. On the other hand, NO^-₃origins in branch rivers of the Yamato river are various combinations of (A) and (B). The NO^-₃origins of branch rivers were determined by whether the flux of NO^-₃ increased with the flow rate or not. On the other hand, CF concentration in the Yamato river water is considered to strongly depend on the amount of domestic sewage. Although the flow rate in the river changed remarkably due to heavy rains, the flux of CF remained unchanged because the volume of domestic sewage did not change even on a rainy day.