Water quality and aquatic insect were investigated over a year in the River Tamoki where river improvement works were conducted from 1991 to 98. Recovery of aquatic insect based on the diversity index by Shannon was late where supply of aquatic insect from the upper stream is resicted by a soil saving dam and the river bed was covered with foot protection blocks. On the other hand, it was fast where loose and settled stones with several centimeters and emerged plants are present. It was concluded that a soil saving dam and bed materials are important factors to recover water environment in rivers at which improvement works were carried out.
