Phosphates are chemicals containing the element phosphorous and come from a range of sources when present in water. Runoff from fertiliser is one contributor with others including human and animal sewage, chemical manufacturing and fruit and vegetable processing. One of the largest contributors of phosphorous to water bodies, however, is soil erosion. When bank erosion occurs during flooding or soil is not held down by rooted plants, it can transport significant amounts of phosphorous into the water.
This affects water quality by causing excessive growth of algae which clouds the water and is known as an algal bloom. The algae feed on the phosphorous which cause them to grow out of control in water ecosystems and create imbalances, reducing the dissolved oxygen, threatening other life forms and producing dangerous toxins.