Abstract
The effect of river pollution by the Ashio Copper-Mine, near Nikkô in Tochigi Prefecture, upon the aquatic insects was examined. The insect samples were collected quantitatively at ten stations in the Watarase-gawa system, which receives the effluents of the Mine at Station 3. The amounts of copper and zinc dissolved in the river water increase rapidly at St. 6, where there were found two kinds of insect larvae, a caddis worm, Polycentropits sp. and a stonefly nymph, Acroneltria stiginatica. The effect of river pollution is distinct the aquatic insects decrease markedly in both the number of species and of individuals. In St. 9 and 10, 27 km and 38 km respectively, distant from the effluents of the Mine, it seems to recover the aquatic fauna to a certain extent.
