sentences:  At times of low flow in the River Exe, water is released into the river for abstraction downstream at Tiverton and Exeter.The effects of this regulation of the water flow from the lake have been studied by comparing the regulated River Haddeo and the neighbouring (unregulated) River Pulham.It showed that the main thermal effects of impoundment and regulation have been to raise mean water temperature, eliminate freezing conditions, depress summer maximum values, delay the annual cycle and reduce diurnal fluctuation.