About Ontojarvi Dam

Ontojärvi is a regulated lake in the Kainuu region of eastern Finland, forming part of the Oulujoki river system. Covering around 90 square kilometres, the lake was brought under regulation in 1951 as part of the same post-war hydropower programme that transformed the entire Oulujoki basin. The reservoir holds approximately 250 million cubic metres. Ontojärvi is connected to the broader Oulujoki system through the Ontojoki river and feeds into a series of downstream power stations. The surrounding Kainuu region is characterised by vast boreal forests, and the Ontojärvi basin forms part of the larger wilderness landscape that makes Kainuu one of Finland's least densely populated and most pristine regions. The lake supports fishing for pike, perch, and brown trout, and the shoreline forests are valued for elk and bear hunting. Water level fluctuations from hydropower regulation have shaped the character of the shoreline over decades, creating characteristic drawdown zones.