Freshwater monitoring across the globe: the role of citizen science within the European Water Framework Directive (WFD) and the United Nations Sustainable Development Goals (SDGs), and opportunities to incentivize the collaboration with environmental regulators.

Citizen science plays a crucial role in advancing the objectives of the European Union's Water Framework Directive (WFD) and the United Nations Sustainable Development Goals (SDGs). Among the key strengths of citizen science is that it fills information gaps in the management and observation of aquatic ecosystems, especially small rivers that often lack national and sub-national agency monitoring. The present study explores opportunities and challenges of integrating citizen science data with those of Environmental Agencies. The current state of the art is discussed through an analysis of 85 publications dealing with freshwater citizen science, finding that 34 of the ones individuated actually use citizen-science generated data. These 34 studies were analysed in more details focusing on data quality and geographical distribution. Findings highlight that citizen-generated data reach an accuracy between 70% and 90% when compared to laboratory values, but despite this outcome there is often lack of trust in citizen science data and processes. This is reflected in a limited involvement with policymakers and regulatory agencies. The present publication highlights good practices, challenges and opportunities for collaboration with environmental agencies, giving examples of some projects to address the WFD and increase the impact of freshwater citizen science.