Many causes of pollution including sewage and fertilizers contain nutrients such as nitrates and phosphates. In excess levels, nutrients over stimulate the growth of aquatic plants and algae. Excessive growth of these types of organisms consequently clogs our waterways, use up dissolved oxygen as they decompose, and block light to deeper waters. This, in turn, proves very harmful to aquatic organisms as it affects the respiration ability or fish and other invertebrates that reside in water.
Pollution is also caused when silt and other suspended solids, such as soil, washoff plowed fields, construction and logging sites, urban areas, and eroded river banks when it rains. Under natural conditions, lakes, rivers, and other water bodies undergo Eutrophication, an aging process that slowly fills in the water body with sediment and organic matter. When these sediments enter various bodies of water, fish respirationbecomes impaired, plant productivity and water depth become reduced, and aquatic organisms and their environments become suffocated. Pollution in the form of organic

Material enters waterways in many different forms as sewage, as leaves and grass clippings, or as runoff from livestock feedlots and pastures. When natural bacteria and protozoan in the water break down this organic material, they begin to use up the oxygen dissolved in the water. Many types of fish and bottom-dwelling animals cannot survive when levels of dissolved oxygen drop below two to five parts per million. When this occurs, it kills aquatic organisms in large numbers which leads to disruptions in the food chain.

1 Pesticides
Pesticides that get applied to farm fields and roadsides—and homeowners' lawns—run off into local streams and rivers or drain down into groundwater, contaminating the fresh water that fish swim in and the water we humans drink. It's tempting to think this is mostly a farming problem, but on a square-foot basis, homeowners apply even more chemicals to their lawns than farmers do to their fields! Still, farming is a big contributor to this problem. In the Midwestern United States, a region that is highly dependent on groundwater, water utilities spend $400 million each year to treat water for just one chemical—the pesticide Atrazine.

2 Fertilizers and nutrients pollution
Many causes of pollution, including sewage, manure, and chemical fertilizers, contain "nutrients" such as nitrates and phosphates. Deposition of atmospheric nitrogen (from nitrogen oxides) also causes nutrient-type water pollution.
In excess levels, nutrients over-stimulate the growth of aquatic plants and algae. Excessive growth of these types of organisms clogs our waterways and blocks light to deeper waters while the organisms are alive; when the organisms die, they use up dissolved oxygen as they decompose, causing oxygen-poor waters that support only diminished amounts of marine life. Such areas are commonly called dead zones.
Nutrient pollution is a particular problem in estuaries and deltas, where the runoff that was aggregated by watersheds is finally dumped at the mouths of major rivers.

3 Oil spills
Oil spills like the Exxon Valdez spill off the coast of Alaska or the more recent Prestige spill off the coast of Spain get lots of news coverage, and indeed they do cause major water pollution and problems for local wildlife, fishermen, and coastal businesses. But the problem of oil polluting water goes far beyond catastrophic oil spills. Land-based petroleum pollution is carried into waterways by rainwater runoff. This includes drips of oil, fuel, and fluid from cars and trucks; dribbles of gasoline spilled onto the ground at the filling station; and drips from industrial machinery. These sources and more combine to provide a continual feed of petroleum pollution to all of the world's waters, imparting an amount of oil to the oceans every year that is more than 5 times greater than the Valdez spill.
Shipping is one of these non-spill sources of oil pollution in water: Discharge of oily wastes and oil-contaminated ballast water and wash water are all significant sources of marine pollution, and drips from ship and boat motors add their share. Drilling and extraction operations for oil and gas can also contaminate coastal waters and groundwater.
As for gasoline and gas additives, leaking storage tanks are a big problem. The US Environmental Protection Agency (EPA) estimates that about 100,000 gasoline storage tanks are leaking chemicals into groundwater. In Santa Monica, California, wells supplying half the city's water have been closed because of dangerously high levels of the gasoline additive MTBE.
4 Mining

Mining causes water pollution in a number of ways:
· The mining process exposes heavy metals and sulfur compounds that were previously locked away in the earth. Rainwater leaches these compounds out of the exposed earth, resulting in "acid mine drainage" and heavy metal pollution that can continue long after the mining operations have ceased.
· Similarly, the action of rainwater on piles of mining waste (tailings) transfers pollution to freshwater supplies.
· In the case of gold mining, cyanide is intentionally poured on piles of mined rock (a leach heap) to chemically extract the gold from the ore. Some of the cyanide ultimately finds its way into nearby water.
· Huge pools of mining waste "slurry" are often stored behind containment dams. If a dam leaks or bursts, water pollution is guaranteed.

5 sediment
When forests are "clear cut," the root systems that previously held soil in place die and sediment is free to run off into nearby streams, rivers, and lakes. Thus, not only does clearcutting have serious effects on plant and animal biodiversity in the forest, the increased amount of sediment running off the land into nearby bodies of water seriously affects fish and other aquatic life. Poor farming practices that leave soil exposed to the elements also contribute to sediment pollution in water.

6 chemicals and industrial procsses
Almost all bodies of water in the world have some level of pollution from chemicals and industrial waste.
In the United States, 34 billion liters per year (60%) of the most hazardous liquid waste—solvents, heavy metals, and radioactive materials—is injected directly into deep groundwater via thousands of "injection wells." Although the EPA requires that these effluents be injected below the deepest source of drinking water, some pollutants have already entered underground water supplies in Florida, Texas, Ohio, and Oklahoma.

7 personal-care products and household cleaning products
Whenever we use personal-care products and household cleaning products—whether they be laundry detergent, bleach, or fabric softener; window cleaner, dusting spray, or stain remover; hair dye, shampoo, conditioner, or Rogaine; cologne or perfume; toothpaste or mouthwash; antibacterial soap or hand lotion—we should realize that almost all of it goes down the drain when we do laundry, wash our hands, brush our teeth, bathe, or do any of the other myriad things that incidentally use household water. Similarly, when we take medications, we eventually excrete the drugs in altered or unaltered form, sending the compounds into the waterways. Studies have shown that up to 90% of your original prescription passes out of you unaltered. Animal farming operations that use growth hormones and antibiotics also send large quantities of these chemicals into our waters.
Unfortunately, most wastewater treatment facilities are not equipped to filter out personal care products, household products, and pharmaceuticals, and a large portion of the chemicals passes right into the local waterway that accepts the treatment plant's supposedly clean effluent.
Study of the effects of these chemicals getting into the water is just beginning, but examples of problems are now popping up regularly:
· Scientists are finding fragrance molecules inside fish tissues.
· Ingredients from birth control pills are thought to be causing gender-bending hormonal effects in frogs and fish.
· The chemical nonylphenol, a remnant of detergent, is known to disrupt fish reproduction and growth.

8 Sewage
In developing countries, an estimated 90% of wastewater is discharged directly into rivers and streams without treatment. Even in modern countries, untreated sewage, poorly treated sewage, or overflow from under-capacity sewage treatment facilities can send disease-bearing water into rivers and oceans. In the US, 850 billion gallons of raw sewage are sent into US rivers, lakes, and bays every year by leaking sewer systems and inadequate combined sewer/storm systems that overflow during heavy rains. Leaking septic tanks and other sources of sewage can cause groundwater and stream contamination.
Beaches also suffer the effects of water pollution from sewage. The chart below shows the typical reasons that about 25% of the beaches in the US are put under water pollution advisories or are closed each year. It's clear that sewage is part of the problem, even in what is supposedly the most advanced country in the world.

9 CO2
Long study of the role of man-made CO2 in the earth's oceans found that the oceans had absorbed enough CO2 to already have caused a slight increase in ocean acidification. The fear is that further CO2 uptake will increase acidification even more and cause the carbonate structures of corals, algae, and marine plankton to dissolve. This could have significant impacts on the biological systems of our oceans.

10 Heat
Heat is a water pollutant—increased water temperatures result in the deaths of many aquatic organisms. These increases in temperature are most often caused by discharges of cooling water by factories and power plants.
Global warming is also imparting additional heat to the oceans. The impact on marine life is unknown at this point, but it's likely to be significant.

There are many different types of water pollution with varying effects on the environment. Water is one of the most important world resources and is essential to all aspects of life.
Water covers 70 percent of the earth’s surface and is important for both people and the environment. The pollution of water has wide reaching effects it harms wild life and the environment, effects the availability of drinking water and many precious resources are used in the cleaning of polluted water.
Different Types of Water Pollution
Water pollution takes many forms. Although there are natural causes of water pollution, for instance that caused by volcanoes and other natural phenomenon, the pollution caused by man is of the greatest concern.
1. Biological Water Pollution
Some viruses and bacteria are water born. These can cause serious diseases in people in direct contact with this contaminated water. This might include people drinking, swimming or washing in the contaminated water and extremely serious and contagious diseases such as cholera and typhoid are spread in this manner.
2. Oxygen Depletion
Oxygen depletion destroys the natural balance of the water and ultimately bacteria thrive and fish and other wildlife die. Oxygen depletion is caused by the release of biodegradable matter into the water, such as sewage and the natural process of breaking this down uses the oxygen in the water. Once all the oxygen has been depleted, bacteria are able to take over making the water polluted.
3. Nutrients
Nutrients such as phosphorus and nitrogen are essential to plant growth. Fertilizers contain many nutrients and when these enter the water supply, perhaps due to water running off a field into a river, the nutrients cause an imbalance in the make up of the water. As nutrients are important to plant growth on land, the same applies to plants in the water. Therefore, too many nutrients in the water encourage the growth of weeds and algae. This can make the water highly polluted and result in oxygen depletion as mentioned above.
The growth of algae is also known as a bloom, and the bright green spread of an algae bloom in fresh water is easily recognizable.
4. Chemical
Chemical water pollution is perhaps the type of water pollution that we are most familiar with. This term is used to describe the act of adding unwanted chemicals to the water and is done through the accidental spillage of substances into water, waste from factories or industry and through pesticides running off fields into water.
Chemicals in water are poisonous and harmful to wildlife as well as making the water too polluted to drink. The effects of chemical pollution are wide reaching.

Chemical water pollution is also used to describe the pollution of water by oil, for instance when an oil tank ruptures or a ship sinks. The photographs and images we see on the television of oil covered birds and dying wildlife gives some indication of the serious nature of this and other types of pollution.
5. Suspended Matter
Not all chemicals and pollutants are water soluble, and those that aren’t are called suspended matter. The tiny particles of matter stay in the water and eventually fall to the bottom, forming a layer of silt on the floor of the lake or river. This is harmful to wildlife and causes long term problems due to an imbalance in the natural infrastructure of the water. In addition to the problems caused by the suspended matter, the problem caused by pollution due to suspended matter is compounded by dead fish and wildlife decomposing in the water.