Nidau is a municipality in the Biel/Bienne administrative district in the canton of Bern in Switzerland.

Biel/Bienne District is an administrative district in the Canton of Bern, Switzerland. It is located along both shores of the northeastern half of Lake Biel and is part of the Seeland administrative region, and its capital is Biel/Bienne. It contains 19 municipalities with an area of 97.63 km2 (37.70 sq mi) and a population of 90,536, over half of which lives in the district's capital. While it is the smallest district in surface area, it has the third largest population in the canton.