St. Peter's Island is a peninsula and former island situated in Lake Biel in the canton of Bern, Switzerland. It has a length of about 5 kilometres (3.1 mi) and a maximum width of 800 metres (2,600 ft). Its highest point is 474 metres (1,555 ft) above sea level or 45 metres (148 ft) above lake level. It was formed in the last Ice Age, when the Rhône Glacier reached as far as the Jura mountains. It is a promontory of the Jolimont, above Erlach. Politically the island is split between the municipalities of Erlach and Twann-Tüscherz, the largest part belonging to the latter municipality.

Twann was a municipality in the district of Nidau in the canton of Bern in Switzerland. On 1 January 2010 the municipalities of Tüscherz-Alfermée and Twann merged into the municipality of Twann-Tüscherz.