Background
Citizen science has helped to expand chemical monitoring of the UK freshwater environments. Given the continuous reductions in monitoring budgets for regulators, such as the Environment Agency, community involvement provides an opportunity to monitor rivers at the spatial and temporal resolutions needed for effective water quality management.
The Focus on Freshwater Quality
The primary focus of many UK citizen science initiatives has been on understanding freshwater health, particularly through the monitoring of nutrient pollution. High levels of nitrates and phosphates - often from agricultural run-off and wastewater - are key indicators of ecological stress leading to eutrophication. Volunteers, equipped with simple, standardised testing kits, take samples from a number of sites, building up a detailed, real-time map of water quality that informs conservation action and policy.
More recently, citizen science has been used to monitor micropollutants, including pharmaceuticals, pesticides, and illicit drugs. Projects now often incorporate high-tech laboratory analysis of volunteer-collected samples to identify these contaminants, with results often revealing concerning levels of substances like imidacloprid (from pet flea treatments) and various antibiotics and antidepressants in waterways nationwide.
An excellent example of a citizen science initiative to understand chemical pollution is the Great Water Blitz, coordinated by Earthwatch Europe. This is a large-scale, biannual campaign that mobilises thousands of citizen scientists across the UK over a single weekend to take snapshots of water quality. The campaign primarily uses simple testing protocols to measure nitrate and phosphate levels, providing a picture of nutrient pollution across river basin districts. Through partnerships with academic institutions, such as Imperial College London, subsets of samples have been analysed using advanced mass spectrometric analysis. This collaboration links basic, high-volume field data with cutting-edge chemical residue analysis, demonstrating the powerful synergy between community action and professional science.
The Catchment Systems Thinking Cooperative (CaSTCo), led by the Rivers Trust and partners, is a more systemic, long-term approach to integrating citizen science data into decision-making. CaSTCo’s goal is to create a national, standardised framework for collaborative monitoring, ensuring volunteer-collected data is of known quality and comparable with official monitoring. CaSTCo helps community groups move beyond basic screening to collect "Tier 1" data that can be used for reconnaissance, and by applying a "weight of evidence" approach, it aims to ensure citizen science results are trusted and influential enough to be incorporated into regulatory practices. This program focuses heavily on quality assurance, providing auditing of methods, and developing open data platforms, ultimately empowering volunteers to drive evidenced-based action for river recovery.
The data generated by citizen scientists—whether through short, intensive blitzes or sustained monitoring—is invaluable. It highlights pollution hotspots, identifies chemicals posing a risk to aquatic life, and provides the evidence base needed to push for better regulation and investment in infrastructure. As this field evolves, citizen science is increasingly poised to tackle even more complex challenges, including the widespread monitoring of "forever chemicals" (PFAS), ensuring a truly comprehensive understanding of the health of the UK's vital freshwater resources.
Simon Browning from the Rivers Trust talks about how citizen science can be used to understand chemical contamination of rivers.
Key Reading
Earth Watch (2025) Great UK Water Blitz
Environment Agency (2025) Supporting citizen science: Technical Advisory Framework