THE RIVER GREAT OUSE, A HIGHLY EUTROPHIC, SLOW-FLOWING, REGULATED, LOWLAND RIVER IN EASTERN ENGLAND

In this paper we aim to provide a brief historical perspective and acc ount 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 tim es the Great Ouse supported a great abundance and diversity of fish an d until well into the present century was regarded as one of the premi er mixed cyprinid fisheries of England. More recently, the fishery has declined substantially and is now heavily dominated by small roach wh ile some other formerly abundant species, notably common bream, have d eclined markedly. There are few quantitative long-term data available to establish the time period over which this decline occurred but ther e is a common perception that it was accelerated during the 1970s; a p eriod of extensive engineering works that included the restoration of the previously derelict navigation system up to Bedford. Backwaters th at are subject to less disturbance than the main river channels genera lly support a more diverse and abundant fauna, suggesting that physica l 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 conditio ns in the modern river are suited to the needs of larval and juvenile cyprinids. (C) 1997 by John Wiley & Sons, Ltd.