Wikipedia
Noktundo is a former island in the delta of the Tumen River on the border between Primorsky Krai and North Korea. The area of the island was .
In the 15th century, Noktundo belonged to the Jurchen. In 1587 there was a battle fought on this island between the local Jurchen and the invading army from Yi Sun-sin, a general of Korea.
At the time of the shallowing of the northern branch of the Tumen, the course of the river changed from time to time. As a result, the island of Noktundo was sometimes joined with the mainland of Primorsky Krai. Regardless, the island remained under Korean jurisdiction.
The island was under Qing control until 1860 Convention of Peking, the Qing Dynasty ceded the island to the Russian Empire. This became a matter of protest to the Koreans, who claimed that the Qing had no authority to do so. In 1990, the former Soviet Union and North Korea signed a border treaty which made the border run through the center of the river leaving territory of the former island on Russian side. South Korea refused to acknowledge the treaty and demanded that Russia return the territory to Korea.