 This was a periglacial lake of the Devensian glacial period, fifteen or twenty thousand years ago.The ice sheet closed the natural drainage from the Vale of Pickering, the Humber and The Wash so that a lake of a complex shape formed in the Vale of Pickering, the Yorkshire Ouse valley, the lower Trent valley and the Fenland basin.This valley was its spillway into the southern North Sea basin, thence to the English Channel basin.