The objective of REBECCA is to provide underpinning for one of the key scientific principles on which the Water Framework Directive (WFD) is based, i.e. that relationships between the biological state and physical and chemical properties of surface waters are sufficiently well understood to enable the management of catchments and rivers to achieve ecological objectives. Historically, there has been great success in maintaining and improving the quality of surface waters by developing and understanding of the links between anthropogenic pressures (e.g. water abstraction, agriculture, and effluent discharges) and the chemical status of waters, although there remain many challenges in reliably designing and implementing the necessary programmes of measures. Our present understanding of the link between chemical properties and ecological state, while good in some instances, is generally not adequate to support management intervention against ecological objectives.