Introduction to nutrient pollution and Nutrient Neutrality

Dorset is home to many areas that are internationally important for wildlife, including estuaries and freshwater habitats. Excess nutrient levels in protected estuaries and freshwater habitats increases algal growth leading to a loss of biodiversity.

In our area nutrient inputs into the hydrological catchments of these estuarine and freshwater habitat sites comes from two main sources, agriculture, and treated wastewater effluent from development. This pollution has left the habitats in an unfavourable condition and makes them extremely sensitive to further nutrient pollution.

We must consider the impact of new development on these habitats, and as part of this take account of their existing condition, when making planning decisions. In March 2022, Natural England advised us and other councils around the country, that development within the catchments of the protected habitat sites effected by nutrient pollution has the potential to worsen their condition. Natural England advocated an approach of Nutrient Neutrality where applicants use mitigation to offset the increase in nutrient load that would arise from their development.

The requirement for Nutrient Neutrality only applies where the increase in nutrient loading arising from the development is significant. This includes:

  • any form of development that increases overnight stays within the catchment
  • some commercial development that either attract large numbers of people into the catchment (such as a tourist attraction) or where there is a significant discharge into the catchment for example from an industrial process
  • development which results in the intensification of agricultural practices, such as an additional cattle barn

Development that increases overnight stays in the catchment may comprise permanent residential development, gypsy and traveller development, care homes, nursing homes, tourist accommodation including both permanent and temporary campsites and hotels.

More detailed information about nutrient pollution and Nutrient Neutrality is available on our Nutrient pollution and the law page.

More detail on the affected catchments is available on the following dedicated pages:

Since the updated advice from Natural England was released, we have been working to help support nutrient neutrality in the effected catchments in our area to enable development to take place. The government have put in place legislation and other measures to reduce the mitigation burden on development so that much-needed new homes can be delivered.

These measures include:

  • requiring the upgrade of wastewater treatment works through the Levelling Up and Regeneration Act 2023 (Part 7 of the Act refers to the nutrient pollution standards and government has prepared an ‘Nutrient neutrality update’ following announcements on nutrient neutrality)
  • providing funding for a Natural England led nutrient mitigation scheme to deliver nutrient mitigation in priority catchments (see government’s written ministerial statement and Natural England’s blog post on their nutrient mitigation scheme)
  • the Local Nutrient Mitigation Fund to enable councils to deliver nutrient neutrality mitigation (government has published details of the outcomes of the first round of bids for the fund and of opportunities for a second round of biding)

Wastewater treatment works upgrades

For those nutrient sensitive catchments designated on 25 January 2024 (Notice of designation of sensitive catchment areas 2024 - GOV.UK (, the Levelling Up and Regeneration Act places a duty on water companies to upgrade the performance of certain wastewater treatment works to achieve higher permitting requirement (known as a technically achievable limit) by April 2030. Government issued a notice and maps. There are exemptions to the upgrading requirements in the Act which can be widened so that they apply to more wastewater treatment works or narrowed so that they apply to fewer wastewater treatment works. The Secretary of State announced the exemptions on 24 May 2024.

The new permitting requirements for wastewater treatment works are, in most cases, significantly lower than the current permit levels and therefore where they are applied the mitigation burden on development will be reduced in the longer term as nutrient concentrations in wastewater discharges are reduced. Despite this there is still likely to be a need to mitigate the impacts of the remaining nutrients in wastewater after the upgrades have been applied. Please refer to the pages relating to Poole Harbour for explanation around the implications for exemptions for nutrient neutrality in this catchment. This mitigation will need to be secured in perpetuity (i.e. 80 years) through appropriate planning conditions or legal agreements depending on the circumstances.

Where development receives planning permission before the upgrade date, this creates a need for temporary mitigation to bridge the period from the date of the planning permission to the upgrade date. Where permission is granted after the upgrade date temporary mitigation will not be required. The amount of temporary mitigation needed will be calculated using the appropriate calculator for the catchment with the temporary mitigation being secured through the necessary legal arrangements or planning conditions depending on the circumstances.