Research and analysis

Nutrient futures for Windermere: summary

Published 20 May 2026

Applies to England

1. Chief Scientist’s Group report summary

This study investigated how future climate change could impact the water quality of Windermere in the English Lake District. The project estimated how climate change affects the movement of nutrients through the catchment and the growth of microscopic lake water plants called phytoplankton. Three management options were tested to determine if reducing nutrient inputs to lakes could counteract climate impacts on phytoplankton communities. Understanding these impacts will help the Environment Agency and others adapt nutrient regulation to better protect lakes in future.  

1.1 Background

Nutrients are critical to aquatic life, but too much can lead to excessive growth of naturally occurring phytoplankton. Excessive phytoplankton can harm aquatic life and present a human health risk, limiting the use of lakes for drinking water, recreation and tourism. In many places, nutrient inputs have increased in catchments through human activities such as land use, land management and wastewater discharges. Climate change may also exacerbate phytoplankton growth.

1.2 Approach

The study linked a catchment water quality model and lake phytoplankton model to describe the relationship between catchment nutrient supply and phytoplankton growth in Windermere and Esthwaite Water. This relationship was subjected to climate change and three nutrient reduction scenarios, which projected how phytoplankton communities would respond in future years (2076 to 2079). The nutrient reduction scenarios were:

• scheduled water company improvements to water quality
• reduced nutrient contributions from the agricultural sector
• stopping all nutrient inputs from wastewater treatment

Model outputs included the amount (biomass) of phytoplankton in the lakes. The project compared the biomass to World Health Organisation thresholds (WHO10) for cyanobacteria (phytoplankton that can produce harmful toxins) to indicate the risk posed to human health. While models cannot provide an exact representation of complex lake processes, they are useful tools to better understand how lakes will function in future.

1.3 Results

Climate change altered the load, concentration and timing of nutrient inputs to the lakes. Total yearly nutrient loads increased a small amount (up to 7%) by 2076 to 2079. Nutrient concentrations entering the lakes increased by between 4 and 33% varying by nutrient type and lake basin. Nutrients were most concentrated in summer, which is the main phytoplankton growing season. Climate change also drove the proliferation of cyanobacteria in summer, when the risk to human health is amplified by increased recreational activity. Climate change therefore led to an increase in WHO10 exceedances in both lakes in future compared to the present.

All three nutrient management scenarios had a positive outcome, leading to fewer days a year above the WHO10 threshold than in the present day. Prevention of all wastewater discharges entirely counteracted the expected climate change impacts in Winderemere. Reduced nutrient inputs improved the status of Windermere and Esthwaite Water, as defined by the Water Framework Directive. However, the levels of cyanobacteria in Esthwaite Water indicated a risk to human health under all future management scenarios.

1.4 Conclusions

While there will be impacts on lakes the results show that local nutrient management can reduce the pressures placed on lake environments by global climate change. The same scenarios had different impacts in the different lakes. The factors controlling this were lake size and shape as well as different catchment land use, history and nutrient sources. This highlights the importance of tailoring management actions to specific lake characteristics.

Climate change will continue to affect the nature of Windermere and other lakes facing similar nutrient pollution pressures. This combination of catchment and lake modelling illustrates how the Environment Agency and others can explore the effectiveness of intervention measures, taking a multi-sector approach to regulate nutrient pollution in future.

1.5 Publication details

This summary relates to information from project SC420004, reported in detail in the following output:

• Report: SC420004/R
• Title: Nutrient futures for Windermere
• Project manager: Sarah Fell, Chief Scientist’s Group
• Research Contractor: Alex Elliott, UK Centre for Ecology and Hydrology

This project was delivered by the Environment Agency’s Chief Scientist’s Group, which provides scientific knowledge, tools and techniques to enable us to protect and manage the environment as effectively as possible.

Enquiries: research@environment-agency.gov.uk.

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