Potential impact of groundwater augmentation of river flows on fisheries: a case study from the River Ouse, Yorkshire, UK

Many lowland rivers in the UK are under increasing pressure from abstraction of water for potable supply or irrigation. Many schemes, both existing and proposed, attempt to mitigate the loss of flow by augmentation from upstream reservoirs or pumping of groundwater into adjacent rivers. The impact of flow regulation by reservoirs is well documented, but little attention has focused on the effect of groundwater augmentation on the biota, particularly fisheries, in the receiving river. The present paper examines the potential effects of pumping groundwater into minor tributaries of the Yorkshire Ouse in England on the cyprinid fisheries downstream of the discharge points and in the main river channel. Concerns were raised with respect to poor water quality and reduced water temperature. In particular, it was predicted that small reductions in river water temperature brought about by discharge of cold (≤ 10 °C) groundwater could have serious detrimental effects on cyprinid fish recruitment and juvenile growth in the receiving river, leading to a decline in stocks.