The harmful effects of water pollution are :
(i) Addition of undersirable substances such as fertilizers, pesticides, mercury salts used in paperindustries. This results in change in both physical and chemical characteristics of water.
(ii) The polluted water may contain disease- causing harmful bacteria such as cholera, typhoid, etc.
(iii) Removal of dissolved oxygen adversely affect the aquatic organisms.
(iv) Any change in temperature affect the breeding of aquatic organisms.
(v) The eggs and larvae of various animals are particularly susceptible to temperature changes.