Background – Penwith Downs Moors and Heaths in west Cornwall has been submitted for possible SSSI designation. The potential SSSI site consists of 55 units and Natural England have gathered much supporting evidence for the proposed designation. One of the key features is valley mires and further hydrological information is required for three of the potential units that contain valley mire habitat: Boswens North (survey site 24), Boswarva Carn to Great Bosullow (survey site 28), and Bussow Moor (survey site 54). In addition to these three proposed valley mire units a further unit named Bostraze Bog was hydrologically surveyed by Rigare Ltd (2018).