These metals were locked up in mineral matter under neutral pH levels, but become mobile when the pH lowers. Metal can clog fish gills causing breathing complications or cause deformities to young fish. They can also settle on the stream bottom filling in spaces between rocks where insects live or eggs are laid, even smothering these eggs. Human Impact Acidic waters have been and continue to be a major environmental concern. Whereas unpolluted precipitation has a pH of about 5.6, the precipitation in most of the Northeast United States has a pH of between 4 and 4.5.
Air pollution is the cause.
Waterways may not be affected by this acidic rain if the geology in the watershed contains a lot of acid-neutralizing rocks containing CaCO3. However, a region void of this type of rock and low alkalinity can have streams that are damaged by acid rain. The waste material of coal mining is called spoils or overburden and is the discarded soil and crushed rock found above and between coal seams. As in many chemicals, there is no distinct dividing line between safe and harmful pH levels. Natural waters should have a pH between 5.0 and 8.5, since lower or higher values are likely to be harmful to fish populations and other aquatic life.