Guide
Nutrient neutrality catchments: which areas are affected, and why they move
Updated
The list is short, public and specific. What catches people out is that a catchment boundary follows drainage rather than administrative geography, and that both the boundaries and the calculators behind them are revised.
Where the list comes from
The catchments are published by Natural England and the Department for Environment, Food and Rural Affairs in the gov.uk guidance Using the nutrient neutrality calculators, which sets out 27 nutrient neutrality catchments alongside the nutrient that applies to each and whether the catchment is also designated as nutrient sensitive (gov.uk). Our table above reproduces that list as published on the date shown.
Why the boundary is not the council boundary
- It follows water. A catchment is the area draining to the protected site, so a boundary can run through a town, and two sites a street apart can fall on opposite sides of it.
- The treatment works matters as much as the site. Where a scheme connects to the mains, the relevant question is which wastewater treatment works serves it and where that works discharges. Gov.uk records that following the March 2026 revision, wastewater treatment works discharging outside the revised nutrient neutrality catchment were set to zero in the River Camel and River Eden calculators.
- Councils publish the working boundary. The local planning authority applies the advice and publishes the map for its area. That is the copy to use.
- It has changed and will change again. Gov.uk records boundary changes in March 2026 following review of the Water Industry National Environment Programme, and in May 2025 the removal of the River Wensum calculator because it is included in the renamed Broads and Wensum SACs calculator.
Nutrient sensitive designation is a different thing
Some catchments are additionally designated as nutrient sensitive. Gov.uk explains that a designated sensitive catchment area is one in which the water company must upgrade wastewater treatment works serving a population equivalent of over 2,000 to meet specified nutrient removal levels under the Water Industry Act 1991, and that the calculators automatically take those upgrades into account. That is why the mitigation requirement for the same scheme can fall over time in a designated catchment: the baseline is improving underneath it.
How the calculation is put together
Gov.uk describes each catchment calculator as a cover page plus five worksheets: nutrients from wastewater, nutrients from current land use, nutrients from future land use, nutrients removed by sustainable drainage systems, and a final nutrient budget which combines them and adds a buffer. Inputs include the date of first occupancy, occupancy rate, daily water usage, the number of residential units, the wastewater treatment works name, soil drainage type, annual average rainfall, nitrate vulnerable zone status and land cover before and after development. Some local planning authorities also have their own calculators. None of this is a spreadsheet exercise to be attempted casually: the inputs carry planning consequences and the outputs get scrutinised.
If your site is anywhere near a boundary, get the council's written confirmation of which side it falls on before you spend money on anything else. Run the checker to see what follows from the answer.