River flow data are the foundations of water management. Hydrometric data are required for resource assessments, regulatory purposes, river management and, in a digested form, to direct policy development and help draft legislation. As with much environmental monitoring, the need for river flow data becomes particularly compelling during periods of actual or anticipated change. As yet, there is limited evidence of flow regime changes attributable to global warming but most scenario-based climate change projections suggest that the broad hydrological stability which characterised the 20th century may not continue through the 21st. However, climate change is but one of a number of driving forces which can affect river flow patterns, others include changes in land use, agricultural practices and patterns of water use. Similarly, the information needs of an increasingly broad community of river flow data users evolve through time in response to changes in, for example, the legislative framework, national policy objectives, and the increasing engagement of a range of stakeholders in water issues and management.