Koitajoki (or the Koita River) (Russian: Койтайоки) is a river in Eastern Finland and partly in Russia in Northern Europe. Having its origin just by the international boundary in Ilomantsi of Northern Karelia in Finland, the Koitajoki River enters the territory of the Republic of Karelia in Russia, to return to Finland some 30 kilometres (19 mi) further south. It then flows northwest through the Petkeljärvi National Park and the Kesonsuo bog area, and further downstream receives the outflow from Lake Koitere.