Agriculture: Agricultural production often emits pollutants that affect the quality of water resources Activities that can contribute to water pollution include confined animal facilities, grazing, plowing, pesticide spraying, irrigation, fertilizing, planting, and harvesting. The major agricultural pollutants that result from these activities are sediment, nutrients, pathogens, pesticides, and salts. Agricultural activities also can damage habitat and stream channels.

Atmospheric Deposition: Atmospheric deposition occurs when pollutants in the air fall on the land or water. Pollution deposited in snow, fog, or rain is called wet deposition, while the deposition of pollutants as dry particles or gases is called dry deposition. Air pollution can be deposited into water bodies either directly from the air onto the surface of the water, or through indirect deposition, where the pollutants settle on the land and are then carried into a water body by runoff or through natural processes such as the movement of groundwater through the soil. Any chemical that is emitted into the air can become an air deposition problem. Some of the common ones include different forms of nitrogen (in high concentrations), mercury, copper, polychlorinated biphenols (PCBs), polycyclic aromatic hydrocarbons (PAHs), chlordane, dieldrin, lead, lindane, polycyclic organic matter (POM), dioxins, furans, toxaphene, hexachlorobenzene, hexachlorocyclohexane, and diazanon. Even chemicals that are no longer in use in the U.S. (such as PCBs) can be deposited because they are emitted from incinerators that burn contaminated garbage or from contaminated sites, or blown in from other countries.

Construction: Activities associated with construction, land developement, or road maintenance that contribute to non point source pollution, particularly increased sedimentation due to land disturbances.

Contaminated Sediments: Sediments are soils, sand and other matter that wash from land and settle on the bottom of a river, lake, bay or the ocean floor. Sediment at many sites throughout the United States was polluted years ago by chemicals such as DDT, polychlorinated biphenyls (PCBs), and mercury. These pollutants may accumulate in fish and may cause increased risks of cancer, neurological and IQ impairment in people who eat large quantities of contaminated fish. While use of these substances has been banned or restricted for many years, these chemicals can persist for many years in the sediment, and continue to be a source of concern for the environment and public health. Other chemicals that are released to surface waters from industrial and municipal discharges and polluted runoff from urban and agricultural areas continue to accumulate to harmful levels in sediments.

Combined Sewer Overflows: Combined sewer overflows (CSOs) are remnants of the country's early infrastructure. In the past, communities built sewer systems to collect both storm water runoff and sanitary sewage in the same pipe. During dry weather, these "combined sewer systems" transport wastewater directly to the sewage treatment plant. In periods of rainfall or snowmelt, however, the wastewater volume in a combined sewer system can exceed the capacity of the sewer system or treatment plant. For this reason, combined sewer systems are designed to overflow occasionally and discharge excess wastewater directly to nearby streams, rivers, lakes, or estuaries. CSOs contain not only storm water but also untreated human and industrial waste, toxic materials, and debris. This is a major water pollution concern for cities with combined sewer systems. CSOs are among the major sources responsible for beach closings, shellfishing restrictions, and other water body impairments. Combined sewer systems serve roughly 950 communities with about 40 million people. Most communities with CSOs are located in the Northeast and Great Lakes Regions, particularly in Pennsylvania, Indiana, Ohio, Illinois, Michigan, New York, West Virginia, and Maine.

Industrial Point Sources: Pollution by industrial sources from discharges, runoff, and land treatment of wastes.

Land Disposal: Intentional land based disposal of wastewater, sewage, sludge, and hazardous waste that makes it way into waterbodies as well as unintended contamination from landfills and leachate.

Marinas: Marinas are located right at the water's edge, so there is a strong potential for marina waters to become contaminated with pollutants generated from the various activities that occur at marinas, such as boat cleaning, fueling operations, and marine head discharge, or from the entry of storm water runoff from parking lots and hull maintenance and repair areas into marina basins.

Hydromodification/Habitat Modification: Habitat modifications include activities in the landscape, on shore, and in waterbodies that alter the physical structure of aquatic ecosystems and have adverse impacts on aquatic life. Examples of habitat modifications to streams include: removal of streamside vegetation that stabilizes the shoreline and provides shade, which moderates instream temperatures; excavation of cobbles from a stream bed that provide nesting habitat for fish; stream burial; and excessive suburban sprawl that alters the natural drainage patterns by increasing the intensity, magnitude, and energy of runoff waters.
Hydrologic modifications alter the flow of water. Examples of hydrologic modifications include channelization, dewatering, damming, and dredging.

Municipal Point Sources: Discharges from publicly owned waste water treatment plants.

Natural Sources: Natural sources refer to an assortment of water quality problems, including natural deposits of salts, gypsum, nutrients, and metals in soils that leach into surface and ground waters; warm weather and dry conditions that raise water temperatures, depress dissolved oxygen concentrations, and dry up shallow waterbodies; and low-flow conditions and tannic acids from decaying leaves that lower pH and dissolved oxygen concentrations in swamps draining into streams.

Nonpoint Sources: Nonpoint source (NPS) pollution comes from many diffuse sources. NPS pollution is caused by rainfall or snowmelt moving over and through the ground. As the runoff moves, it picks up and carries away natural and human-made pollutants, finally depositing them into lakes, rivers, wetlands, coastal waters, and underground sources of drinking water. These pollutants include: excess fertilizers, herbicides, and insecticides from agricultural lands and residential areas; oil, grease, and toxic chemicals from urban runoff and energy production; sediment from improperly managed construction sites, crop and forest lands, and eroding streambanks; salt from irrigation practices and acid drainage from abandoned mines; and bacteria and nutrients from livestock, pet wastes, and faulty septic systems.

Impairment source not reported: There was no cause information reported to EPA.

Other Sources: The source of the impairment cause was reported, but does not belong in any of the other source categories reported by scorecard.

Resource Extraction: Resource extraction activities, including surface and subsurface mining, are industrial operations that takes place in the natural environment, potentially disturbing large amounts of material and land area. The potential adverse effects of these activities on water quality include; acid mine drainage, the drainage that results from sulfide oxidation in rocks exposed to air and water; erosion and sedimentation, the process by which soil particles are detached, suspended, and transported from their source of origin; chemical releases, such as cyanide which is used in leaching of relatively low-grade ores that otherwise would not be economically feasible; and hydrologic changes, due to the massive quantities of water necessary for many processes can disrupt surface water and groundwater flows.
The removal of water from mine workings can also result in drawdown. Drawdown can reduce the amount of water available for recharging wetlands and surface water, thereby affecting any organisms that depend on those waters.

Septic Systems: An on-site system designed to treat and dispose of domestic sewage. A typical septic system consists of a tank that receives waste from a residence or business and a system of tile lines or a pit for disposal of the liquid effluent (sludge) that remains after decomposition of the solids by bacteria in the tank.

Silviculture: Silviculture (forestry) activities impair water quality through the removal of streamside vegetation, road construction and use, timber harvesting, and mechanical preparation for the planting of trees. Road construction and road use are the primary sources of non point source pollution on forested lands, contributing up to 90 percent of the total sediment from forestry operations. Harvesting trees in the area beside a stream can affect water quality by reducing the streambank shading that regulates water temperature and by removing vegetation that stabilizes the streambanks. These changes can harm aquatic life by limiting sources of food, shade, and shelter.

Unknown Sources: The source of the impairment cause was not able to be determined.

Urban Runoff/Storm Sewers: The porous and varied terrain of natural landscapes like forests, wetlands, and grasslands trap rainwater and snowmelt and allow it to slowly filter into the ground. Runoff tends to reach receiving waters gradually. In contrast, nonporous urban landscapes like roads, bridges, parking lots, and buildings don't let runoff slowly percolate into the ground. Water remains above the surface, accumulates, and runs off in large amounts. Cities install storm sewer systems that quickly channel this runoff from roads and other impervious surfaces. Runoff gathers speed once it enters the storm sewer system. When it leaves the system and empties into a stream, large volumes of quickly flowing runoff erode streambanks, damage streamside vegetation, and widen stream channels. In turn, this will result in lower water depths during non-storm periods, higher than normal water levels during wet weather periods, increased sediment loads, and higher water temperatures. Native fish and other aquatic life cannot survive in urban streams severely impacted by urban runoff. Urbanization also increases the variety and amount of pollutants transported to receiving waters. Sediment from development and new construction; oil, grease, and toxic chemicals from automobiles; nutrients and pesticides from turf management and gardening; viruses and bacteria from failing septic systems; road salts; and heavy metals are examples of pollutants generated in urban areas. Sediments and solids constitute the largest volume of pollutant loads to receiving waters in urban areas. When runoff enters storm drains, it carries many of these pollutants with it. In older cities, this polluted runoff is often released directly into the water without any treatment. Increased pollutant loads can harm fish and wildlife populations, kill native vegetation, foul drinking water supplies, and make recreational areas unsafe.