Liquid waste pouring from pipe into flowing river. (United States Environmental Protection Agency. Reproduced by permission.)

Freshwater pollution is the contamination of inland water (not saline) with substances that make it unfit for its natural or intended use. Pollution may be caused by fecal waste, chemicals, pesticides, petroleum, sediment, or even heated discharges. Polluted rivers and lakes are unfit for swimming or fishing; polluted water is unsafe to drink.

Background

For centuries, fecal waste and other pollutants were dumped in rivers, with "dilution the solution" to pollution. In the mid-twentieth century, many American rivers and streams were open sewers, choking on everything from human waste to highly toxic industrial discharges. New York City alone pumped a half billion gallons of raw sewage into its harbor every day. As pollution levels grew, so did the impacts. "No swimming" signs became the norm. Lake Erie was...