Oulujärvi (Finnish: [ˈou̯luˌjærʋi]) or Lake Oulu or Ule (Swedish: Ule träsk), is a large lake in the Kainuu region of Finland.

It is also historically known as Lake Cajania from a former name of Kainuu.

[3] With an area of 928 square kilometres (358 sq mi) it is the fifth largest lake in the country.

Its nickname is the "Kainuu Sea", and it is bordered by the three municipalities of Vaala, Paltamo, and Kajaani.

This Oulu Province location article is a stub.