Lake Vansjø with its many islands and skerries is the largest lake in Østfold County. Its shores are framed by forests, farming country and housing. It presents all types of terrain, ranging from mountain slopes and reed beds to rolling forested areas. Lake Vansjø touches on Moss, Våler, Rygge and Råde municipalities in Østfold County.
Lake Vansjø is divided in two sections, one the shallow Vanemfjorden Bay to the west and to the east the deeper Storfjorden Bay. The two sections are separated by a narrow sound. Lake Vansjø is relatively eutrophic, evidenced by the periodic summertime blue-green algal blooms. A popular recreation site, the lake is offers opportunities for boat life, canoeing, swimming and sports fishing.