However, when misused, the adverse impacts can be extensive. This is a specialist subject and local knowledge will be important. A high nutrient level is essential for productive agriculture. However, the use of both natural and chemical fertilizers may result in an excess of nutrients which can cause problems in water bodies and to health. Nitrates are highly soluble and therefore may quickly reach water bodies.
Phosphates tend to be fixed to soil particles and therefore reach water courses when soil is eroded.
Phosphate saturated soils and high phosphate level groundwater are now found in some developed countries. The two parameters to which fish are most sensitive are temperature and dissolved oxygen. Oxygen is less soluble in water at higher temperatures. Also more non-ionized ammonia, which is toxic to fish, moves into solution from as the temperature rises as well as with an increase in pH. The higher the ambient temperature, the closer fish are living to their upper tolerance limit and the less able they are to tolerate changes to their environment. Organic pollution will reduce the dissolved oxygen content of the water.