( 1 )In Britain, man's alteration to river habitats began with forest clearances and continued with developments for water power and navigation. Industrialization and population increase led to extensive pollution in lowland rivers. Land drainage greatly reduced wetland habitats and, with headwater impoundment and flood protection works, further modified physical conditions.( 2 )Since the middle of the twentieth century, domestic and industrial pollution have been reduced, but eutrophication and acidificati...