One of the most alarming forms of air pollution is acid rain. It results from the release into the atmosphere of sulphur and nitrogen oxides that react with water droplets and return to earth in the form of acid rain, mist or snow. Acid rain is killing forests in Canada, the USA, and central and northern Europe. (Nearly every species of tree is affected.) It has acidified lakes and streams and they can't support fish, wildlife, plants or insects. (In the USA 1 in 5 lakes suffer from this type of pollution).