Case study: A nature-based solution – reducing nutrients into Windermere
An example of how the Wonderful Windermere scheme is helping others
United Utilities has been working with South Cumbria Rivers Trust to help YMCA Lakeside, on the shores of Windermere, improve its existing wastewater treatment system.
In a great example of how working together we can help have a positive impact on the lake’s water quality, the improvements at YMCA Lakeside have successfully reduced the amount of phosphorus which would have reached the waterbody.
What was the solution?
The assessment of the system used to treat wastewater from the site at YMCA Lakeside suggested that a nature-based solution, developed and delivered by South Cumbria Rivers Trust in partnership with United Utilities, could be the way to improve performance.
The solution has been designed to be sympathetic to the environment, consisting of three individual stages.
- First stage: The waste from the site enters via a newly a constructed wetland that helps with sediment removal.
- Second stage: This waste is then passed through to the reactive media bed, which is the primary means of removing phosphorus. This bed is covered in reed beds (seen in the image above).
- Third and final stage: This is an attenuation pond, which provides additional protection to the receiving watercourse.
The whole system improves water quality going into Windermere, whilst also boosting biodiversity and providing an enhanced habitat for wildlife.
Measuring its success
Once in place, the team started a sampling programme to compare the treated wastewater quality before and after the new technology was introduced.
The results below show the sample data for the first phase of the project during intensive 2-week sampling. Additional data samples are being collected throughout 2026.
This data has been independently assured.
|
Sample number |
Date sample taken |
Date of Analysis |
Pre-intervention P (mg/l) |
Post-intervention P (mg/l) |
|
1 |
20.11.25 |
20.11.25 |
1.09 |
0.1 |
|
2 |
21.11.25 |
21.11.25 |
1.14 |
0.08 |
|
3 |
24.11.25 |
24.11.25 |
0.81 |
0.07 |
|
4 |
25.11.25 |
25.11.25 |
0.71 |
0.07 |
|
5 |
26.11.25 |
26.11.25 |
0.31 |
0.06 |
|
6 |
27.11.25 |
27.11.25 |
0.09 |
0.07 |
|
7 |
28.11.25 |
28.11.25 |
0.42 |
0.07 |
|
8 |
01.12.25 |
01.12.25 |
0.10 |
0.06 |
|
9 |
02.12.25 |
02.12.25 |
0.14 |
0.07 |
|
10 |
03.12.25 |
03.12.25 |
0.10 |
0.06 |
|
11 |
04.12.25 |
04.12.25 |
0.14 |
0.07 |
|
12 |
05.12.25 |
05.12.25 |
0.15 |
0.07 |
What are the outcomes?
We have assessed what the annual benefit of this project is in terms of kilograms of phosphorus removed per year from the system used at YMCA Lakeside and an independent assurer has validated the annual benefit calculated.
The model set out in the Wonderful Windermere scheme methodology how we calculate phosphorus reductions from private septic systems, the summary of which can be viewed below:
|
Calculation |
Value |
Unit (1) |
Explanation |
|
Per Capita Phosphorus |
0.00142 |
Kg/hd/d |
STW Load kg/y (1.14) / 365 / average occupancy (2.2) = 0.00142 Kg/hd/d |
|
Per capita water usage per day |
150 |
l/hd/d |
|
|
Expected crude concentration |
9.47 |
mg/l |
Derived from Per Capita Phosphorus and Water Usage Per Day (1.42g P in 150 litres of wastewater per day) |
|
Removal efficiency of Reactive (adsorptive) Media |
65 |
% |
Removal rate – Table 3, Wonderful Windermere Methodology Document |
|
Flow to Reactive (adsorptive) Media |
6.61 |
m3/d |
Expected average flow |
|
Total removal per annum |
12.57 |
Kg P/yr |
Sum of the daily P Load removed (kg/d). Assumes no occupancy beyond 14th November |
(1) Units: kg/hd/d = kilogram per head per day; l/hd/d = litres per head per day; mg/l = milligrams per litre; % = percentage; m3/d = metres cubed per day
Year one results
For year one of this scheme, United Utilities had a target to deliver an improvement to the Windermere catchment of 9.5kg of phosphorus removed.
As per the modelling calculations above, we have outperformed that target and achieved a benefit of 12.57kg in Year 1 – subject to final regulatory approval, expected later in 2026/27.
What's next?
We’re committed to helping others improve their septic systems or land manage to help reduce phosphorus in Windermere and excited to collaborate with new partners on more projects like this. We will continue to monitor the system at YMCA Lakeside with South Cumbria Rivers Trust to understand how it continues to perform.
More information on the Wonderful Windermere scheme and how we’ve performed will be made available in United Utilities’ Annual Progress Report published by 1st September 2026.