<P> Nonpoint source pollution refers to diffuse contamination that does not originate from a single discrete source . This type of pollution is often the cumulative effect of small amounts of contaminants gathered from a large area . A common example is the leaching out of nitrogen compounds from fertilized agricultural lands . Nutrient runoff in storm water from "sheet flow" over an agricultural field or a forest are also cited as examples of non-point source pollution . </P> <P> Contaminated storm water washed off of parking lots, roads and highways, called urban runoff, is sometimes included under the category of non-point sources . However, because this runoff is typically channeled into storm drain systems and discharged through pipes to local surface waters, it becomes a point source . </P> <P> The specific contaminants leading to pollution in water include a wide spectrum of chemicals, pathogens, and physical changes such as elevated temperature and discoloration . While many of the chemicals and substances that are regulated may be naturally occurring (calcium, sodium, iron, manganese, etc .) the concentration usually determines what is a natural component of water and what is a contaminant . High concentrations of naturally occurring substances can have negative impacts on aquatic flora and fauna . </P> <P> Oxygen - depleting substances may be natural materials such as plant matter (e.g. leaves and grass) as well as man - made chemicals . Other natural and anthropogenic substances may cause turbidity (cloudiness) which blocks light and disrupts plant growth, and clogs the gills of some fish species . </P>

What are the effects of water pollution wikipedia