containing over one-fifth of the world's fresh surface water. Numerous smaller lakes dot northern Russia and Siberian plains. The largest of these are lakes Belozero, Topozero, Vygozero, and Ilmen in the country's northwest and Lake Chany in southwestern Siberia. A number of other rivers drain Siberia from eastern mountain ranges into the Pacific Ocean. The Amur River and its main tributary, the Ussuri, form a long stretch of the winding boundary between Russia and China. The Amur system drains most of southeastern Siberia. Three basins drain European Russia. The Dnieper, which flows mainly through Belarus and Ukraine, has its headwaters in the hills west of Moscow. The 1,860-kilometer Don, which is the fifth-longest river in Europe, originates in the Central Russian Upland south of Moscow and then flows into the Sea of Azov at Rostov-on-Don. The Volga, widely seen as Russia's national river due to its historical and cultural importance, is the longest river in Europe, it rises in the Valdai Hills west of Moscow and meandering southeastward for 3,510 kilometers before emptying into the Caspian Sea. Altogether, the Volga system drains about 1.4 million square kilometers. Linked by several canals, western Russia's rivers long have been a vital transportation system; the Volga remains the country's most commercial river, and carries about two-thirds of Russia's inland water traffic. Agriculture geography One billion acres of land is arable in Russia, but only about 0.1 percent is permanent agriculture. The landscapes of region have extremely varied environments because of the following: Tundra landscapes cover most of the region, where conditions are harsh because of the cold climates, and plant life is not very well supported to grow because of the harsh conditions. This has become a problem, as the unfavorable conditions make agriculture more difficult. Mountain ranges are spread through the region, such as the Ural Mountains, which have become the dividing line between European Russia and Eurasian Russia. European Russia also has the European plains which extend about 2,000 miles. The workforce involved in agriculture workforce was reported to be about 9.4% of the population in 2016. The main export of Russia is grain, which is about 6% of the world trade. Other exported products include fish and oil with 3%, meals with 2%, and meat which accounts for less than 1%. Pre-industrial agriculture Agriculture has always been important for Russia. The land was worked by its peasant class. Climate The