Natural England's assessments during 2019/20 suggest that more than 3000 hectares of the intertidal parts of Chichester Harbour, which is the subject of several European designations, is now classified in an "unfavourable - declining" condition.  Water quality is a contributing factor to the build-up of excess nutrients in the Harbour causing eutrophication (algal growth) which impacts on the Harbour's ecology and conservation.

Sewage from new development using waste water treatment works or an on-site package treatment plant that discharges to Chichester Harbour contributes to the excess nutrients in the Harbour (albeit in small amounts relative to other sources) and therefore needs to be considered in line with the Habitats Regulations.  This means that before agreeing to a proposal (such as a planning application or a development plan) the authority needs to undertake a Habitats Regulations Assessment and be satisfied that the proposal will not have any adverse impact on the protected site or sites.  Certain types of new development will now need to be nutrient neutral to avoid detrimental harm to the Harbour's ecology and conservation.  

Guidance

Natural England has published detailed guidance on achieving nutrient neutrality (updated June 2020) which includes a methodology for calculating the "nutrient budget" of proposed development.  As part of the information needed to determine planning applications, if a relevant proposal (primarily those involving an overnight stay) is likely to discharge into Chichester Harbour, then a nitrogen budget will need to be prepared and submitted with the planning application.  Natural England's Guidance sets out when and how nutrient neutrality must be achieved with catchment maps to clarify the areas that are affected.