In this paper we aim to provide a brief historical perspective and account of prevailing conditions in the River Great Ouse as background to detailed research, carried out by the Institute of Freshwater Ecology and the Freshwater Biological Association since 1989.
In medieval times the Great Ouse supported a great abundance and diversity of ®sh and until well into the present century was regarded as one of the premier mixed cyprinid ®sheries of England. More recently, the ®shery has declined substantially and is now heavily dominated by small roach while some other formerly abundant species, notably common bream, have declined markedly. There are few quantitative long-term data available to establish the time period over which this decline occurred but there is a common perception that it was accelerated during the 1970s; a period of extensive engineering works that included the restoration of the previously derelict navigation system up to Bedford. Backwaters that are subject to less disturbance than the main river channels generally support a more diverse and abundant fauna, suggesting that physical conditions, rather than water quality, are primarily responsible for restricting biological diversity and productivity in the main river. Subsequent research, reported in the series of papers that follow, has therefore focused on the extent to which physical and biotic conditions in the modern river are suited to the needs of larval and juvenile cyprinids.