Question

dissolved oxygen level of a reservoir is drastically reduced due to the industrial wastes released to it immediate consequence of this will be?

Answer 1

Aquatic life will be disbalanced. Fish uses the dissolved Oxygen for breathing.

Answer 2

Fish and other aquatic life such as plants, weeds, will perish. Apart from this, the usable water in the reservoir will reduce and the water cannot be used as such for domestic purposes without proper treatment.