Vansjø is a lake in the municipalities of Moss, Råde, Rygge, Våler in Østfold county, Norway. Vansjø is part of Moss watershed stretching from Østmarka. Vansjø has four inflow rivers. The lake is fed by the Hobølelva which drains lake Sværsvann, Veidalselva which originates in Hobøl as well as Svinndalselva and Mørkelva which originate in Våler.