Novosibirsk Reservoir or Novosibirskoye Reservoir , informally called the Ob Sea , is the largest artificial lake in Novosibirsk Oblast and Altai Krai, Russian Federation. It was created by a 33 m high concrete dam on the Ob River near Novosibirsk. The dam, built in 1956, is for generating hydroelectric power. The reservoir is 200 km long and up to 17 km wide. Its area is 1,070 km² and its volume is 8.8 km³. Its average depth is 8.3 m. The design hydroelectric power output is 460 MW, the average energy production is 1,687 GWh per year.