Agriculture plays a significant role in the quality of water and three factors come into play when considering agricultural effects: pesticides, fertilizers and the waste produced by farm animals. When pesticides or fertilizers are applied to crops the excess materials will either run off the land, or seep into the groundwater, with an eventual ending in bodies of water such as lakes, ponds, or streams. The excess nutrients, including nitrates and phosphates, contaminate freshwater ecosystems causing eutrophication and algae blooms, which limits sunlight reaching lower waters, and reduces dissolved oxygen. Dr. Robert Diaz of VIMS and WRI staff says there are more than 228 large coastal areas affected by serious eutrophication, for example Wamberal Lagoon in Australia and Izmir Bay in Turkey. Point sources of contamination to ground water can also include septic tanks, fluid storage tanks, landfills, and industrial lagoons. If a contaminant is soluble in water and reaches the water table, the contaminant will be transported by the slowly moving ground water, and possibly end up in surface water bodies nearby, poisoning the water an organisms in it. Human waste may contain harmful elements that can cause human disease such as E. coli which will spread through the groundwater system and into the food web. Not only do these problem affect the quality, but if a large water storage area is contaminated the availability of clean water will be decreased.
Atmospheric deposition of chemicals, such as sulphate and nitrate, can cause some surface-water bodies to become acidic. Acid rain can be caused by industrial emissions from factories and power plants that burn fuels such as natural gas, coal or oil, emit smoke that gives off oxides of sulphur and nitrogen is one cause. Natural causes only account for 10% of the pollution causing acid rain. When acidic precipitation enters lakes and river