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Major Types of Nonpoint Source Pollutants

There are many major types of nonpoint source pollutants that can and are harming the quality of streams, rivers, and lakes across Indiana. Read further to understand what these pollutants are and what activities can cause them to get into our water.

E. coli

Escherichia coli (E. coli) is a common bacterium found in the digestive track of all warm-blooded animals. E. coli, like many other kinds of bacteria, is not always harmful to humans. However, because it is relatively easy and economical to monitor for E. coli and because it is often found in conjunction with bacteria that do make humans sick, E. coli is often used as an indicator that waters are polluted with animal or human waste.

In agricultural environments, sources of E. coli include straight-piped sanitary lines, failed septic systems, livestock manure, and wildlife. E. coli from human sources is not a common source of water pollution in most urban environments. Sanitary sewer systems help protect water from human originated E. coli, and communities around the state are addressing combined sewer overflows (CSOs) to further protect water quality. CSOs are direct discharges of untreated sewage which occur when storm water run-off is too much for a community’s combined sanitary and storm sewer system to handle. Suburban and rural areas are more likely to have septic systems, which can be an E. coli source if they are not well maintained, placed too close together, or used in the wrong type of soil. Animal waste also contributes to E. coli and pathogens in surface waters. A major source of E. coli in some urban and suburban areas is pet waste. Pet waste left on lawns and impervious surfaces can be washed into storm sewers and waterways.


The term "nutrients" refers to nitrogen and phosphorus. Streams and lakes with high nutrient levels can promote excessive plant and algal growth. When the plants and algae die, the dead and decaying vegetation depletes the water's oxygen supply. This, in turn, leads to the death of fish and other aquatic organisms. This phenomenon can occur in stagnant streams, small ponds, or across larger waterbodies. Nitrogen readily dissolves in water and is often directly transported from field to stream through drainage tiles or from lawns through storm sewers. Phosphorus is less soluble in water, but attaches to soil particles, allowing it to enter waterbodies through sediment run-off.

Nutrients affect human health. Consuming excessive levels of nitrate, a form of nitrogen often found in fertilizer, can cause serious illness and sometimes death. In infants, the conversion of nitrate to nitrite by the body can interfere with the oxygen-carrying capacity of the child’s blood. Indiana water is tested for nitrogen before it can be used as a drinking water source by public water facilities. However, many residents in rural Indiana drink from privately-owned wells. These homeowners must arrange to get their wells tested for nitrates and other potential contaminants of concern, such as pesticides and arsenic.

Lawn and agricultural fertilizers are the primary source of nutrients. Nutrients are also found in animal and human waste, which means sources of E. coli also contribute nutrients.


Sediment is the loose sand, clay, silt, and other soil that settles to the bottom of a waterbody. The U.S. Environmental Protection Agency lists sediment as the most common pollutant in rivers, streams, lakes, and reservoirs. When sediment enters a waterbody, it smothers valuable aquatic breeding ground, damages fish gills, fills in stream channels (which increases the chance of flooding), contributes to the erosion of stream banks, decreases the recreational value of the waterbody, and can be costly for drinking water treatment plants to filter out. In addition, sediment often carries nutrients with it into Indiana streams and lakes.

While natural erosion produces nearly 30 percent of the total sediment in the United States, erosion from human use of land accounts for the remaining 70 percent. In agricultural watersheds, the most significant source of sediment is tilled fields. Farm fields, especially when conventional tilling is used, lack a continuous layer of vegetation to hold the soil in place, so sediment run-off is a major concern. Improperly managed construction sites also contribute significant amounts of sediment to local waterways; up to 25 times that of agricultural lands (Chesters, 1979) and 2,000 times that of forested lands (EPA 833-F-00-008, R 12/2005 [PDF]). Construction activities that disturb an acre or more of land are subject to Indiana Rule 5 and Indiana Rule 13, which limit the amount of sediment that is permitted to leave a construction site. Another significant source of sediment comes from domestic animal activity. Without proper management, livestock can over-graze creating pasture erosion, and trample streambanks.

Excess Flow

Flow refers to the amount of water moving through the stream. Excess flow can cause downstream flooding and erode stream banks. Although flow is not a “pollutant,” it can cause the movement of greater amounts pollutants such as sediment, nutrients, and bacteria. While it is a large concern in most urban and suburban areas where impervious surfaces make infiltration impossible, excess flow is also a concern in agricultural areas.

In urban areas, storm water that normally would infiltrate into the ground instead travels over impervious surfaces, such as streets, driveways, and sidewalks, and runs directly into storm sewers and water ways. This causes a rapid rise and fall of water levels in urban streams that is referred to as “flashiness.” The fast-moving floodwaters of flashy streams wash the leaves, rocks, and logs that aquatic macroinvertebrates and fish use as habitat downstream. Over time, high water flow will also widen water channels, which may threaten roads and other structures.

Surface run-off and tiled agricultural fields are large contributors to excess flow. Undoubtedly, tiles are important for drainage and the farm economy, but they also move water out of fields and into drainage ditches. This water would have previously infiltrated to the ground water. This run-off water carries sediment and nutrients, and represents more water than Indiana stream channels historically carried. Over time, high water flow will widen water channels, but temporary high flow increases the potential for flooding downstream. When combined with the excess flow from urban and suburban areas, the potential for flooding increases.


Increased water temperature, or “thermal pollution,” may not sound threatening, but it can impede the biological functions of aquatic organisms. The warmer the water, the less dissolved oxygen it can carry; therefore higher temperature results in stress for fish and other aquatic organisms. If high water temperature is sustained for long periods, it can completely change the biological diversity of a stream.

The temperature of a stream is generally regulated by several factors, including the amount of ground water inputs and sun exposure the stream receives. Humans have greatly influenced agricultural streams by removing trees and shrubs from the area adjacent to the stream (known as the riparian corridor). When the stream’s riparian corridor is vegetated with bushes and trees, the shade can help regulate the water temperature and support a healthy biological community. In urban areas, heat is introduced into the stream in two important ways. If the area along the stream bank, known as the riparian corridor, has been depleted of vegetation, there will not be enough shade to keep the water temperature down. If the stream’s riparian corridor is vegetated with bushes and trees, the shade can help regulate the water temperature and support a healthy biological community. A second way that heat may enter the stream is through storm drain outfalls. Rain that has fallen on hot asphalt and other surfaces will be warmer than the water running in the stream, heating it up.


Oils and other chemicals can not only ruin the aesthetics of a waterway, but can also kill aquatic organisms, drastically alter water chemistry, and impact human uses such as recreation and drinking. While industries are the biggest users of oils and chemicals, facilities that use large quantities are required to have a spill response plan to reduce the environmental impact during accidents. In agricultural areas, pesticides and fertilizers make up a potential chemical source. Pesticides and fertilizers improperly stored or applied just before a rain or to frozen ground may run off into the nearest stream. Some chemical applications applied too close to a stream may also “drift” into a stream on wind currents. In urban areas, some of us still pour used or extra oil and other chemicals onto the ground or into storm drains, where it can wash off into surface waters without any kind of treatment, severely impacting waterways.

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