Eikeren or Eikern is a long, deep lake in eastern Norway. The 27.6-square-kilometre (10.7 sq mi) lake is located on the border of Øvre Eiker Municipality in Buskerud county and Holmestrand Municipality in Vestfold county. It is the largest lake in all of Vestfold county, measuring about 16 kilometres (9.9 mi) long and 2.5 kilometres (1.6 mi) wide, and reaching a depth of 158 metres (518 ft).