Stodmarsh Update: “There is no prospect of the nutrients disappearing in the next 5-year period”

“For the foresseable future, it looks like nutrient neutrality is here to stay. There is no prospect of the nutrients disappearing in the next 5-year period”


Stodmarsh is a series of lakes; which is an Internationally designated wetland in unfavourable condition. Some of the lakes are suffering from poor water quality. Nutrient pollution (Nitrates & Phosphates) in the Stour catchment area in Kent are having an adverse effect on Stodmarsh causing eutrophication and algae blooms, which are harming the delicate Stodmarsh ecosystems. Stodmarsh is protected under the The Conservation of Habitats and Species Regulations 2017

Natural England first flagged this issue in July 2020 and ever since it has meant that Local Planning Authorities must carefully consider the impacts of any new developments across six districts which effect the habitat sites at Stodmarsh, and whether those impacts may have an adverse effect on the integrity of the habitat site which requires mitigation. At present, circa 30,000 homes are affected by the nitrate and phosphate issue at Stodmarsh

The impact of the nutrient issue caused by too much nitrate and phosphate in the water has meant that some local planning authorities – Ashford, Dover, Canterbury, Folkestone & Hythe, Maidstone & Swale, are struggling to meet their housing land supply targets. Put simply it means some developments ; which are in the districts mentioned, but outside the Stodmarsh catchment area, are able to get planning persmission through appeals. However, those within the catchment area, its a different matter and it is impacting on some council’s local plans and housing numbers.

On 6 September 22, Southern Water and Natural England officers met with the Chief Planners of Ashford, Canterbury, Dover, Folkestone and Hythe, Maidstone and officers from Kent County Council to discuss Stodmarsh Nutrient Neutrality. This follows Natural England advice on nutrient neutrality which stymies district councils issuing new planning applications. This is significantly impacting construction sector profits, as the number of houses being built is much lower than anticipated.

Through Southern Water’s treatment of water, phosphorus and nitrogen are added to the river. There are other sources (outside Southern Water’s control) which also add nitrogen and phosphorous to the river (e.g., nitrate run-off from the soil due to agricultural use of fertilisers, and groundwater inflow). However, Southern Water’s treatment works are the main contributor of phosphorus to the water (the firm is probably responsible for circa 90% of the phosphorus introduce to the catchment).

The requirement on Southern Water is only to reduce their portion according to their ‘fair share’. As they are not the sole contributor, Southern Water do not have to reduce theirs until the level of nutrients becomes sustainable, rather they only must reduce their portion of the total level of what would be sustainable.

One issue is that the water company is only expected to use something known as ‘Best Available Technology’ or ‘Technical Achievable Limit’. This means that they cannot spend on expensive innovative technology, as ultimately all these costs are funded by the bill payers. There is a limit on what they can do.

Unsurprisingly Southern Water has found for phosphorus, they cannot achieve their fair share of what the acceptable limit for phosphorus is just through using best available technology. They can achieve it, but only by going beyond best available technology, and the costs will be much higher. Southern Water estimate that the scale of investment needed to reach technical achievable limits with best available technology is circa £180m in the next 5 year Annual Maintenance Programme period – 2025/30.

For nitrogen, Southern Water contribute a much smaller portion. Southern Water unsurprisingly cannot achieve their fair share of the nitrogen in any way, even if they go beyond using best available technology.

Consequently, for the foreseeable future, it looks like nutrient neutrality is here to stay. There is no prospect of the nutrients disappearing in the next 5-year period. In short Stodmarsh will continue to have nitrates and phosphates pumped into an internationally recognised wetland, supposedly protected by the Habitats Regulations.

The other issue covered in the workshop of 6th September was the broad strategy. Large sites are going to have to have treatment works on site  probably discharging to a wetland. For most large sites, this should be enough to achieve nutrient neutrality. Smaller sites will not be able to do this, as they will not be able to meet the space requirements, and bespoke treatment works only function at a certain scale. It is not practical or economical, so for smaller sites, the strategy is exploring off-site provision. The main role of KCC as the catchment facilitator is to co-ordinate that piece of work. KCC is looking at various options, the principal option is probably wetlands; there are other options though, such as retrofitting existing housing with low-flow technology that is in the control of the district and borough (social housing). There are also some land-use changes that can help, such as converting agricultural land into woodlands or parklands.

Also, Natural England provided more updates on the funding which the Government announced in  March & July. Natural England said that the competitive funding will not be close to that sum needed; it will be a much smaller pot. Natural England did say that the catchments will be prioritised based on the need, and the Stour is probably one of the highest because of the scale of developments affected (at present, circa 30,000 homes are affected by this issue).

Dover has recently announced that it is no longer required to achieve nutrient neutrality. Kent County Council is checking this with Natural England. Dover District Council has completed a study looking at the Dambridge treatment works (in Wingham), which discharges into one of the tributaries that goes into the downstream catchment for Stodmarsh. Dover District Council has demonstrated that the nutrients introduced there have an insignificant effect at Stodmarsh, which means anything connected to Dambridge no longer needs to reach nutrient neutrality. Kent County Council is waiting for Natural England to formally say what implications this will have for the rest of the downstream catchment. It is not clear yet if nutrient neutrality issues have completely gone away for this area, or not. However, the upstream area would still be affected by the issue.

Local councils are working together on producing a catchment strategy and consultants have been appointed to lead on this; together they’ll be working out the off-site requirement for mitigation based on the principle that larger sites will have on-site treatment works; hoping to receive more information about the competitive bidding process from Natural England so the councils can start putting a collective bid together; work will continue to progress looking at off-site wetland mitigation; and will look at other offsetting opportunities.

Once off-site mitigation is set-up, a credit mechanism will have to be established, to give developers a way of accessing and buying the credits, so they can evidence as part of their planning application that they have offset their nutrients.

So there you have it, Southern Water pleading poverty, while continuing to pollute the environment (which sounds familiar) circa 30,000 homes being held up making a bad situation worse, rents being driven up, and Stodmarsh left to wallow in eutrophication and algae blooms for at least the next five years.

The Shepway Vox Team

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3 Comments on Stodmarsh Update: “There is no prospect of the nutrients disappearing in the next 5-year period”

  1. The South East is already over populated but councils and developers want to encourage more people in – at the expense of locals. Build more homes north and west of London, with building in the South East being for local demand.

  2. This is good news unless your name is Quinn or Monk

  3. ‘This is good news unless your name is Quinn or Monk’. So you don’t live in a house, built by someone, then. So many NIMBY’s occupying housing want to stop others having the same life.

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