When well-designed experiments are performed and analyzed, the controversy may be settled. But the new knowledge derived from well-run experiments also engenders new controversy, and this becomes a part of the creative growth of science. Water pollution was once thought to be a local problem. Now it has expanded to a regional and global problem. Acid rain can cause lakes and forest to dies.
Water tends to tie people together.
The absence or presence of a particular animal species in an aquatic community can often indicate much about the physical conditions and general quality of the habitat. Specifically what it indicates, we are not always sure. Certain species or taxonomic groups have rather specific tolerances to physicals and chemical properties of their habitat, such as temperature, dissolved oxygen content, degree of siltation, stream velocity, degree of pollution, etc. Understanding these relationships is very important information to understand the impact of our actions on the environment. One very important area of research deals with the improvements we try to make.