a river on Sakhalin Island. It measures 350 km. long and drains an area of 7,990 sq km.
The Poronai originates on the western slopes of Mount Nevel’skoi in the Vostochnyi Sakhalin Mountains and flows through a wide marshy valley across the Tym’-Poronai Lowland between the Vostochnyi Sakhalin and Zapadnyi Sakhalin mountain ranges, emptying into Terpenie Gulf of the Sea of Okhotsk. It is fed by snow and rain. There is high water in spring, from April to June, flooding in summer and fall, and a low-water period in winter. The mean flow rate is 120 cu m per sec. The Poronai freezes in November and the ice breaks up in April. The river is a spawning ground for salmon. The city of Poronaisk is at the mouth.