evidence: Meanwhile, China and Russia have also agreed to jointly develop the Bolshoi Ussuriysky Island or Heixiazi Island, which sits at the confluence of two border rivers — the Ussuri and Amur — and ownership is legally shared between Russia and China. It is expected that China and Russia will build a port here to facilitate Sino-Russian trade and benefit the economic development of northeastern China. [...] According to the 1991 Sino-Soviet Border Agreement, China has navigation rights into the Sea of Japan from the Tumen River Estuary. But during the Korean War in the 1950s, Russia and North Korea constructed a rail bridge — named the Korea-Russia Friendship Bridge — over the Tumen River. The vertical clearance level for this bridge is low, which meant that larger vessels would be unable to pass through. It was thus dubbed by the Chinese public as "a river conundrum" (铁索横江).