Which river forms part of the border between North Korea, China and Russia?

The Tumen River is 521 km (324 mi) long that serves as part of the boundary between China, North Korea, and Russia, rising on the slopes of Mount Paekta and flowing into the Sea of Japan. The river flows in northeast Asia, on the border between China and North Korea in its upper reaches, and between North Korea and Russia in its last 17 km (11mi) before entering the Sea of Japan. The river forms much of the Southern border of Jilin Province in North east China and the northern borders of North Korea's North Hamgyong and Ryanggang provinces. The Russian name of the river is Tumannaya, literally meaning foggy. The river is considered the preferred way to cross into China. According to the New York Times, the long, desolate stretches of the Chinese-North Korean border are not patrolled at all. Refugees rarely cross the Tumen into Russia. This is because Russia's short stretch of the river is far better patrolled than China's stretch.