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Every year more and more plants and animals disappear forever. Strangely, it is the most intelligent but most thoughtless animal that is causing most of the problems - man. Nature is very carefully balanced and if this balance is disturbed, animals can disappear alarmingly fast. Every day, thousands of species of animals draw closer to extinction. In many lakes fish are dying. Fishermen are worried because every year there are fewer fish and some lakes have no fish at all. Scientists are beginning to get worried too. What is killing the fish? The problem is acid rain.