The third source of energy is hydro electricity. The region boasts large rivers capable of accommodating in-river hydro plants of 1000 MW and more per project. This potential was realised at an early stage, leading to investigations into the hydro potential of Pamir Tien-Shan and other East Siberian hydro resources. Today these hydro systems contribute roughly 40% of the electricity produced in Russia's Second Electricity Zone (Siberia) and helps to explain why the wholesale electricity prices in Zone 2 are structurally cheaper than in Zone 1 (European Russia).