The Love Windermere partnership is working to bring about a healthier future for the lake and the surrounding area, balancing the needs of nature, the community and the local economy.

Although one of the most studied lakes on the planet, there is much we still don’t know about Windermere.

By taking an evidence and science based approach we will all better understand the most pressing challenges facing the lake and plan effective action to tackle them.

The challenges we face

Over the past 50 years, concerns have been raised about the health of the lake, in particular algal blooms and bacterial pollution, potentially harmful to wildlife and humans.

Nutrients, climate change, extreme weather patterns and the seasonal variations of tourist numbers are all putting the lake and its water quality under increasing pressure.

Windermere: a brief history and outlook


  • Windermere is England’s largest lake, situated in the Lake District National Park which is a UNESCO World Heritage Site.
  • The lake is small on a global scale, but one of the best studied in the world with systematic records dating back to the 1930s, taken initially by the Freshwater Biological Association (FBA), then by the UK Centre for Ecology & Hydrology (UKCEH).
  • Windermere is an exemplar lake that is demonstrating how multiple environmental pressures come together to affect water quality. It may not ever be ‘restored’ in the sense of returning it to some predetermined historical state, but threats can be mitigated to improve conditions and protect the lake for future generations.
  • Long-term data on the lake’s biology and water chemistry are crucial for recommending future management strategies to improve the overall health of the lake and its catchment.

Water quality pressures and their impacts

  • The pressures Windermere faces are many, complex and interacting. Windermere’s sediment record reveals changes since the lake formed around 14,000 years ago, with human actions recognised for at least the last 5000 years (Box 1). Impacts increased in recent centuries and especially after the middle 19th Century. The landscape in which Windermere is situated has undergone a series of substantial changes over the last two centuries, including changes in agriculture and forestry practices as well as growth in tourism and recreation after the railway arrived in 1847 leading to the expansion of the major settlements. Tourism underpins the economy of the central Lake District, with an estimated 7 million visitors to Windermere and its catchment annually (based on 2019 data) increasing inputs to the wastewater system.
  • Nutrient inputs – These come from mains (e.g. wastewater treatment plants, storm overflows) drainage, but also non-mains (e.g. septic tanks operating under General Binding Rules, and permitted septic tanks and package treatment plants) drainage, agricultural run-off (e.g. the use of fertilisers in agriculture can release both phosphorus and nitrogen into the environment), household products (e.g. many laundry, dish and car soaps contain forms of phosphorus) and potentially lake sediment. Elevated levels of nutrients (specifically phosphorus and nitrogen) can influence the ecology and functioning of the lake. For example, nutrient enrichment combined with warmer temperatures has increased the frequency and intensity of potentially harmful algal blooms at the surface and associated deoxygenation at depth in the lake, which has consequences for the health of people, pets, livestock and wildlife.
  • Faecal material inputs – These come from mains and non-mains drainage as well as agricultural run-off. Elevated levels of faecal pathogens can also cause illness in animals, including humans. While microbiological water quality of Windermere at designated sites has continued to be acceptable, faecal pathogens that are present in Windermere as a result of animal husbandry and wastewater are not assessed elsewhere in routine monitoring of water quality.
  • Land use change – Intensive historical land use, including agriculture and forestry operations, is another potential source of sediment, nutrient and bacterial inputs. However, the extent that land use affects water quality depends largely on how the catchment is managed.
  • Invasive non-native species (INNS) – INNS (e.g. roach and ruffe) affect the ecology of the lake, removing zooplankton which eat algae, meaning that algae populations have fewer predators and restrictions on their growth.
  • Climate change – This affects the functioning of the lake directly through warming and weather patterns, but also indirectly by compounding the pressures mentioned above. UKCEH data has shown the surface water temperature of the lake has increased by around 1.7°C over the past 70 years, which will alter the suitability of the lake for different plants and animals, and favour the formation of algal blooms. In addition, increased intensity of rainfall events associated with climate change accelerates the inwash of soil, nutrients and faecal bacteria from the lake’s catchment.

What has been done?

  • Investment by water companies to reduce nutrient inputs has prevented further deterioration. In the early 1990’s, and in response to scientific monitoring and advice, United Utilities installed technology to reduce concentrations of phosphorus at the largest wastewater treatment plants, Ambleside and Tower Wood, which reduced phosphorus inputs to Windermere. The current phosphorus status of the lake has fallen from its peak in 1991 to levels broadly equivalent to those occurring during the 1960s-1970s. Efforts to reduce concentrations further are ongoing.
  • The FBA and UKCEH have been monitoring the lake since the 1930s, including water chemistry and dynamics of phytoplankton, zooplankton and fish populations. High-frequency, automatic monitoring buoys in the North and South Basin of the lake provide hourly data on key parameters. More comprehensive water quality assessments are undertaken seasonally every 5 years. These data have provided insights into how the lake has responded to natural changes, human impacts and actions taken to improve it over seasons, years, and decades.
  • Under the European Union Bathing Waters Directive, the Environment Agency (EA) routinely monitors designated bathing sites for faecal bacteria concentrations. If standards are not met, the EA can demand further wastewater treatment on main effluents.
  • The EA also assesses water quality in accordance with the European Union Water Framework Directive, conducts farm inspections, and has remote monitoring stations on Windermere and the surrounding lakes and rivers to monitor water quality, rainfall, river level, river flow and groundwater level.
  • Further to this, the EA supported the development of the Source Apportionment Geographical Information System (SAGIS), which can help inform understanding of sources of nutrients and chemicals at catchment scale and identify measures to improve water quality in rivers, lakes and estuaries.
  • In 2022, the FBA started the Big Windermere Survey with Lancaster University, which aims to investigate the sources of nutrient and bacterial inputs around the lake shore and wider catchment in order to inform targeted action on the ground. This complements existing monitoring by the EA and South Cumbria Rivers Trust (SCRT). Results show that phosphorus concentrations in Windermere are above target levels (e.g. ‘Good status’ under the European Union Water Framework Directive) but other lakes in the catchment face similar challenges. Levels of faecal indicator bacteria are generally low across seasons, but there are hotspots in summer and autumn and within Windermere.
  • In the same year, the Love Windermere partnership was formed, comprised of 10 partner organisations including the EA, Lake District National Park Authority, FBA (left the partnership in 2024), Lake District Foundation, National Trust, SCRT, National Farmers Union, Westmorland and Furness Council, United Utilities and Cumbria Local Enterprise Partnership. The partnership aims to take a scientific and evidence-based approach to better understand the complex and interdependent pressures facing Windermere and prioritise effective solutions to improve the condition of the lake.

What needs to be done?

  • A better scientific understanding is needed of Windermere’s integrated response to water quality pressures, especially nutrient concentrations, ecological pressures and the ongoing impacts of climate change (e.g. temperature increase, rainfall patterns and water retention time) in order to guide future management and restoration.
  • Any management and restoration of the lake must consider pressures jointly and the combined impacts they may have on the lake. Tackling these issues in isolation may not improve water quality sufficiently to protect the future overall condition of Windermere. A comprehensive approach based on evidence is needed.
  • Improving ecological health will require nutrient inputs from agriculture, private sewage treatment, and wastewater treatment works to be identified and reduced.
  • The roles of Combined Sewer Overflow discharge of untreated sewage at times of heavy rainfall, and animal faecal waste from agricultural land, need to be understood in terms of nutrient inputs and human health.
  • The wider community and local businesses can also make a difference through septic tank maintenance, correct disposal of slurry and waste materials (i.e. not directly into watercourses), using low-phosphorus cleaning products, appropriate use of fertilisers etc.
  • Expected and ongoing climate changes will make Windermere and other lakes much more sensitive to water quality decline than they were in the past. These changes continually shift the historical baseline to which the lake can be restored. Consequently, management and restoration action is needed to maintain the status quo but will need to go further to achieve improvement, including addressing emerging issues. For example, even greater reduction of nutrient concentrations is needed to address this pressure and counter the added effects of climate change. Stricter land management practices may be needed, especially where these will involve riparian zones which help buffer nutrient and faecal material inputs to the lake.
  • Lakes like Windermere are very “patchy” – conditions change a lot with depth, across the lake surface, around the lake shoreline, and over time. Therefore, it is important to take a large-scale and multi-season view of water quality over the long-term. Long-term data on the lake’s biology and water chemistry are key to provide evidence-based solutions to nutrient and faecal material inputs, tourism and its impacts (e.g. pressure on wastewater system, disturbance to wildlife), and climate change (and associated weather patterns).

Box 1. Timeline of events in and around Windermere (YA=years ago)