Summary #
Water pollution occurs when contaminants exceed a watershed’s natural ability to compensate. The two major categories are point source pollution (from identifiable discharge points) and non-point source pollution (from diffuse sources like agriculture, mining, and stormwater). This page describes the major types of water pollution relevant to Pennsylvania watersheds.
Pollution occurs when conditions exceed the watershed’s ability to compensate for the changes. Polluted water may be discolored, possess a coating on the bottom of the stream, or may show no visible sign at all of pollution. There are many different kinds of pollution. The two major categories are Point Source and Non-Point Source pollution.
Point Source Pollution #
Point source pollution comes from a defined, specific source such as a discharge pipe from a factory, municipal sewage treatment plant, or power generating station. The state “Clean Streams Law” as well as the federal Clean Water Act have made great strides towards identifying, controlling and cleaning up point source pollution. This category of pollution still has an effect on today’s watersheds, but not to the great extent as prior to legislation.
Non-Point Source Pollution #
Now that much of the point-source pollution is being controlled, problems are arising that were previously overshadowed. Non-point source pollution (NPS) is being recognized as a major factor in the deterioration of today’s watersheds. NPS pollution is covered by Section 319 of the Federal Clean Water Act. A significant federal and state bureaucracy has been built around NPS and Section 319. It is common to refer to programs or funding simply by using “319” as the qualifier.
Section 319 NPS: http://amrclearinghouse.org/Sub/LEGAL/Section319NPS.htm
Clean Water Act: http://amrclearinghouse.org/Sub/LEGAL/CleanWaterAct.htm
The most common types of non-point source pollution are: AMD, agriculture, erosion and sedimentation, and acid rain. AMD is by far the worst problem facing area watersheds.
Agriculture #
Agriculture is a very serious source of NPS because there are so many kinds of pollution generated. The two most likely pollutants from agriculture are nutrients and sediments. Many of the pesticides and fertilizers used today have a tendency to be washed off of plants and filter into waterways through runoff, increasing nutrient loads. Nutrient and sediment levels increase when unprotected streams run through livestock pastures. Cattle are often the worst of all livestock offenders. They trample the stream sides, increasing erosion and sedimentation. Evidence of nutrient pollution is often seen as algal blooms. These are large pockets of algae that make the water appear almost a soupy green. Blooms have devastating consequences for aquatic organisms. As the algae flourishes on the increase of nutrients (especially nitrogen), the amount of oxygen in the water rapidly decreases to nearly zero. This leaves the water uninhabitable and results in widespread kills of fish and other organisms.
Erosion and Sedimentation #
Erosion and sedimentation are also very common pollutants. Often excess amounts of solids enter waterways because of run-off. Construction sites, fallow fields, and other areas of unprotected soil are extremely prone to large amounts of erosion. Poor forest management practices, such as clear cutting a hillside, can also result in increased erosion. One method of decreasing erosion and sedimentation is with the protection and establishment of riparian buffers.
Riparian Buffers: http://amrclearinghouse.org/Sub/WATERSHEDbasics/Riparian_buffers.htm
Acid Rain #
Acid rain or acid precipitation is becoming a common pollution source. Car exhaust as well as other discharges spout compounds into the air. As clouds form and water vapor mixes with the gases, acids are formed. Sulfuric and nitric acids are the two most commonly found. When the clouds release the water as precipitation, these acids are carried down to earth and drain into unsuspecting waterways. There are times when a stream may appear to be suffering from AMD by the pH level, however no discharge can be found. Acid rain can have the same profound lowering effect on pH as AMD.
Stormwater Runoff #
Storm water runoff is also a problem. Though it may not contain many pollutants, the unrestricted dumping of a large volume of water is detrimental in itself. The streams are accustomed to gradual flow into a waterway, not the forceful rush often associated with storm drains. The extra flow raises levels above the normal, often causing flooding and erosion. The increased flow of water also impacts aquatic habitat, changing the character of the stream from a quiet pool to a rushing, tumbling surge. Many organisms will not inhabit such fast-moving water.
A Watershed Primer for Pennsylvania, produced by the PA Environmental Council: http://www.pecpa.org/_final_pec/WatershedPrimer.pdf
PA Environmental Council: http://www.pecpa.org/
Related Pages #
- Water Quality — Defining water quality
- What is AMD? (AML Basics) — The primary NPS pollutant in PA
- AMD is Nonpoint Source Pollution (AML Basics)
- Riparian Buffers — What Are They? (Watershed 101)
- Land Use — How land use affects water quality
Source and Last Reviewed #
Source: AMR Clearinghouse (amrclearinghouse.org). Migrated to AML-Connect. Last Reviewed: 2026-03-13.
[Admin note: Some external links in this article may be outdated. Verify before relying on them. Flag dead links for removal or replacement.]
Tags: monitoring, assessment, education, amd
