Information on the magnitude and variability of flow regimes at the river reach scale is a central component of most aspects of water resource and water quality management. However, many decisions are made within catchments for which there are no measured flow data. To meet this challenge, a suite of modelling techniques to assist in the estimation of natural and artificially influenced river-flows at ungauged sites has been developed. This paper summarises these models and how they are incorporated within the GIS framework of the Low Flows 2000 software package. The paper will also describe the implementation of Low Flows 2000 within England and Wales by the Environment Agency, and the use of the system in supporting the implementation of the Environment Agency's Catchment Abstraction Management Strategy. This strategy is focused on the delivery of sustainable abstraction licensing and will contribute to the implementation of the Water Framework Directive within England and Wales.