From the beach at Bigbury-on-Sea you can swim around Burgh Island. I think you can do it clockwise or ant-clockwise. The tide will determine the extent of the beach and therefore the length of the swim. This is a more adventurous wild swim due to the possibility of currents and winds, but if done as a group it offers a fantastic experience. The beach to the east has lifeguards some of the time so you can get a bit of advice from them before setting off.