The Obsha is a river in Sychyovsky District of Smolensk Oblast and Oleninsky, Belsky, and Zharkovsky Districts of Tver Oblasts, Russia. It is a left tributary of the Mezha. The Obsha is 153 kilometres (95 mi) long, and the area of its basin 2,080 square kilometres (800 sq mi). The town of Bely is located on the banks of the Obsha.