As threats to wildlife and ecosystems constantly increase, so too does the critical need to use available resources, such as water, more wisely, and to spend conservation money more effectively (Boon, 1992). Demand for long-term ecological information has never been greater if these needs are to be fulfilled. I have been fortunate to spend the whole of my professional life working on an environment I have been in love with ever since I can remember } rivers. Some rivers still appear to support near-natural characteristics, and flora and fauna to match, yet so many others are sad and sorry shadows of their former selves. We know through common sense and centuries of research (Darwin, 1859) that natural selection of species has occurred across the globe, and so too have dramatic changes occurred in the plant and animal communities of rivers in response to natural climate change. For example, rivers in the south-east of Britain have a much richer natural legacy of fish species because they were connected to the freshwater Rhine system less than 15 000 years ago as the last great ice sheets retreated (Davies et al., 2004). In contrast we know surprisingly little about the way riverine communities are affected by natural extremes of recent centuries, or anthropogenically induced ones, and whether these changes are short-or medium-term, or permanent.
This editorial discusses the importance of long-term data sets (LTDs) in science and water management and the role LTDs should play in helping to make sensible river and water management decisions } of paramount importance if we are to sustain water supplies for future human uses without destroying major parts of the planet's environment (Westcoat and White, 2003). It also draws briefly on experiences gathered from working on headwater chalk streams over the past 13 years (Berrie and Wright, 1984;Berrie, 1992;Sear et al., 1999).
The British Antarctic Survey (BAS) (www.antarctica.ac.uk) states that tracing and understanding past changes in the environment play an important role in the prediction of future changes. It was through long-running records collected for over 30 years that BAS scientists first identified the hole in the ozone layer above Antarctica. They note that the Earth is ever changing, and environmental data represent a