Omahaki Sub-Catchment Dashboard

As well as causing direct issues in waterways, sediment (soil particles) can carry phosphorus and pathogens like E. coli with it. Processes and practices that expose soil, or increase its mobility, generate increased levels of sediment. This sediment gets washed into rivers and streams by surface runoff.

Most sediment, phosphorous, and E. coli losses come from a small part of the landscape, called critical source areas. These places may include areas of erosion, stock yards, tracks, races and intensively grazed areas. Other sources of phosphorous and E. coli in streams include fertiliser and animal waste.

The key to preventing these contaminants from entering waterways is to keep your soil where it is, reduce runoff to waterways, and to protect critical source areas.

These are key actions that will reduce the amount of sediment, E. coli and phosphorus entering waterways, to influence better water quality outcomes:

• Exclude stock from the margins and beds of permanent waterways, and from critical source areas. We recommend a five-metre setback from lakes, streams, rivers and creeks. Learn more about stock exclusion, including future exclusion requirements for some waterways on our page: Stock Exclusion.

• Maintain adequate pasture covers on soils vulnerable to sheet erosion.

• Protect your soil. Plan and undertake a programme of tree planting to reduce erosion on vulnerable hill country.

• Strategically break feed winter crops towards waterways, rather than away from them, and do so in parallel to the waterway. This will help to maintain an intercepting wedge of vegetation to catch sediment heading towards the waterways, for as long as possible. All winter forage cropping must have a minimum five-metre buffer from any waterway. More information about regulations is available on our page: Intensive Winter Grazing.

• Use minimum or no-till cultivation where possible, and cultivate across slope rather than up and down. Maintain grass buffers between cultivated paddocks and waterways.

• Manage the runoff from laneways, races and yards where soil and high concentrations of animal excreta are readily mobilised.

• Use sediment traps and bunds to filter and collect sediment in runoff. You can then redistribute this on farm.

• Test your soil before you apply phosphate fertilisers, to prevent excessive applications. Maintain Olsen P at no more than the optimum range.

As well as supporting nuisance plant and algae growth, high levels of dissolved inorganic nitrogen (DIN) can affect stream ecology and can even be toxic to humans and livestock. Unlike phosphorous which attaches itself to soil particles, nitrate generally leaches through the soil and enters streams and waterways via groundwater. The key to minimising nitrogen loss to waterways, is to manage conditions in your paddocks so that excess nitrogen cannot be washed through the soil profile and into freshwater systems.

These are key actions that will reduce the amount of nitrogen entering waterways, to influence better water quality outcomes:

• Budget nutrient use, soil test regularly at block level, and if needed engage specialist help to ensure efficient and effective nutrient application. Excess nitrogen use is costly and can drain through the soil profile and into waterways.
• Apply 'little and often' with split dressings of no more than 50 kgN/ha.
• Avoid the application of nitrogen or effluent when plants are not actively growing (i.e. between May and August), or during periods of high risk (I.e. when heavy rain is forecast, or when soils are saturated). This will reduce excess nitrogen in the soil at times when it is likely to be washed away.
• Retain or enhance shallow, boggy wetlands. Ecosystems like wetlands have very low levels of oxygen, which promotes the removal of nitrates from the water before entering streams and rivers.
• Use feed supplements that have lower concentrations of soluble protein, like maize silage.

The waterways and near-stream habitats in many developed agricultural landscapes no longer support the abundance and diversity of freshwater fish and bug communities that once existed here. Just like humans, bugs and fish need a specific set of things to flourish and thrive. Good and healthy habitat is important, which includes:

• Cool temperatures
• A range of water flows
• Passage along the length of streams so that NZ native fish can migrate
• Riparian vegetation

Bugs and fish also require enough oxygen in the water. Low temperatures, nutrient levels, and sediment levels are important for ensuring good levels of oxygen in the water.

These are key actions that will improve biodiversity in and around your waterways, to influence better water quality and stream health outcomes:

• Address excessive levels of sediment, nutrients and other contaminants entering waterways.
• Maintain minimum flows in permanent streams.
• Address barriers to fish passage.
• Plant appropriate riparian vegetation to shade and cool waterways and shade out excessive plant/algae growth.
• Maintain vegetated strips along the side of waterways to improve in and near-stream habitat.

• Industry-agreed Good Management Practices relating to water quality
• Dairy NZ – Good management Practices for Dairy farms
• Fertiliser Association Code of Practice