Scale of reduction required

This map illustrates the scale of reductions our modelling suggests is needed for each contaminant to take us from the attributes current state (where we are now) to their potential target states (where we want to be).

If you want more detail about how modelling has been undertaken across the region's sub-zones and the assumptions made, check out the reports on the technical reports page on the Oranga Wai website.

We have displayed the scale of the reductions using four colours:

  • Red | Contaminant must reduce between 50% and 100% in this sub-zone
  • Orange | Contaminant must reduce between 20% and 50% in this sub-zone
  • Green | Contaminant must reduce by up to 20% in this sub-zone
  • Blue | Targets for rivers and streams are already met in this sub-zone.

On the map, you will notice some freshwater management units (FMUs) are likely to need more considerable contaminant reductions than others. We acknowledge these reductions might be confronting for some people, but please rememberno decisions have been made to adopt the provisional targets nor, by default, the scale of change displayed here. These maps show us what might be required to realise the aspirations communities have previously told us they want. This engagement is your opportunity to provide further feedback on these matters.

Also, if your sub-zone is blue, where “targets for rivers and streams are already met”, it does not necessarily mean no change is necessary. We must consider how our actions affect people living further down the awa. Human activities that happen upstream, where water quality is typically better, impact the water quality downstream, which tends to be worse.

We have only modelled water quality targets for rivers and streams in the Horizons Region. Work is underway to understand how target states for lakes and estuaries might be set based on the environmental outcomes for each FMU. Once this task is complete, we will evaluate its impact on the modelled reductions. In some areas, this could increase required reductions.

Correction – January 2024: Horizons and our partners have reviewed our modelled reductions and identified some errors, which led to the original reductions for some sub-zones being reported incorrectly. These errors have now been corrected. We sincerely apologise for the errors.

Twenty water management sub-zones have had their category status for total nitrogen reductions changed – 15 now require larger reductions to meet provisional targets, while five require lower reductions.

Thirteen water management sub-zones have had their category status for total phosphorous reductions changed – ten have lower reductions required, while three now require larger reductions.

Eight water management sub-zones now require smaller reductions for E. coli.

If you want specifics on exactly what has changed, please contact us by emailing

How to use the map

Select the contaminant you want to see by choosing an option from the dropdown menu at the top of the map.

Select the buttons on the right to view the information at the regional or FMU scale, or go to your water-management sub-zone by entering your address in the search bar. You can also use the search bar to see the information for less specific addresses, such as a lake or town.

Tap or hover your mouse over a water management sub-zone to see the modelled reductions needed in that area.