Novosibirsk Reservoir or Novosibirskoye Reservoir (Russian: Новосиби́рское водохрани́лище), informally called the Ob Sea (Обско́е мо́ре), 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.