Why are we doing it

All rivers and lakes naturally have nitrogen in them, however, when there is too much nitrogen present, plants are over-fertilised leading to excessive plant growth and algal blooms. These algal blooms may cause skin irritation and be toxic to animals.The main source of nitrogen is farmland, mostly from animal urine. Nitrogen loss happens when nitrogen in the soil is carried to groundwater by rainfall trickling through the soil. The groundwater eventually emerges as surface water, with the nitrogen that leaked from the soil. Nitrogen loss from the soil tends to be highest during autumn and winter and is worse with highly stocked cows on free-draining soils under high rainfall. 

Sediment makes water appear dirty and reduces the amount of light for plants and animals living in the water. Erosion and unstable land, such as slips and gullies or from streambanks, contribute a large amount of sediment to our waterways. Erosion is typically a greater risk in hilly country in the upper catchment or near streambanks. Another source of sediment is races and tracks on-farm.Pest fish, such as koi carp, also aggravate the impact of sediment because they re-suspend sediment in lakes and rivers. Sediment loss occurs when water flows over land before entering waterways. Sediment loss tends to be worse where heavy rain falls onto land that is highly erodible because of the geology, steepness or vegetation cover. 

Phosphorus physically binds to soil, so when sediment is lost, phosphorus is lost too. Phosphorus affects stream life and increases algal blooms, which can make it unpleasant for swimming and drinking. Dung from stock, fertiliser, and erosion are the main culprits for phosphorus loss on-farm. Because phosphorus is found at very low levels in the natural environment, small increases in a waterway can have a big effect on water quality. However, some soils, such as volcanic soils, naturally have a higher phosphorus levels. Phosphorus loss is worse where soils have high phosphorus levels (such as from high phosphorus fertiliser use), and where there is high sediment loss too.

Faecal matter from stock can have a big impact on water quality. Faecal matter contains bacteria, protozoans and viruses that can make both humans and stock sick. Bacteria can enter waterways when animals directly defacate into the waterways or when rainfall carries farm runoff into streams and rivers. Common sources of farm runoff include laneways, stock yards, standing areas, heavily stocked or pugged paddocks and where stock have access to unfenced waterways.