Acid deposition and its effects
Sulfur dioxide and nitrogen oxides from burning fuel form acids in the atmosphere that fall far from the source.
A worked example
A lake at pH 4.0 holds ten times the hydrogen ion concentration of a lake at pH 5.0, enough to kill sensitive fish eggs.
The mistake people actually make
Diluting a pollutant does not remove it, it only spreads it out. The harm comes from the pH change itself and from the aluminium that acidic water releases out of the surrounding soil.