When we think of environmental pollution, we most often conjure up images of smoking factories, toxic waste dumps and oil spills. What we don't realize, however, is that the leading cause of water quality problems is from pollutants that don’t originate from a single source or enter waterways at a particular site. This type of widespread pollution, called nonpoint source pollution, occurs when rainfall, snowmelt or irrigation runs over land, picks up pollutants and deposits t