The principal, over‐arching aim of any catchment management work is to improve the water quality in our freshwater ecosystems and to make a significant contribution to their attainment of good ecological status in accordance with requirements of the EU Water Framework Directive. It is therefore vital that sufficient evidence is collected to provide an objective and robust assessment of the improvements delivered.

In this review, Westcountry Rivers Trust explores the data and evidence available, which, taken together, demonstrate qualitatively and quantitatively that the delivery of integrated catchment management interventions can realise genuine improvements in water quality. To support the evidence collected, they have also summarised a number of case studies which demonstrate catchment management in action.

For each of the main groups of pollutants, identified key sources of pollutant loads and examined the impacts these pollutants have on the aquatic environment, including how they translate into a cost or risk to society. They have also identified key mitigation measures for reducing pollutant loads and evaluated the data and evidence for the efficacy of these measures. This process has also allowed them to identify the interventions for which the evidence of efficacy does not exist or where it does not exist at an appropriate scale.

The review also addresses issues of scale and reviews a selection of modelling tools that can be used to predict the impact of interventions and measures at a larger sub-catchment or whole-catchment scale. It also explores the potential for secondary environmental, economic and societal benefits to result from the delivery of catchment management interventions.

Finally, the governance structures currently being used to implement a catchment management-based approach in the UK are reviewed and some of the approaches now being adopted to create catchment management plans are examined.