In the USSR ‘hydrology’ is a broad term referring to all the waters of the Earth both on the land and in the oceans, while in the United States there is a tendency to confine the science of hydrology to the land only and to leave the hydrologic phenomena of the sea to oceanography.The USSR has some 100,000 rivers over 10 km in length, with a total length of 3,000,000 km or 1,860,00 mi. Four of the rivers of the USSR are among the 15 largest in the world from the standpoint of discharge. The Yenisei has a mean annual discharge of 615,000 cfs; the Lena, 546,000 cfs; the Ob, 441,000 cfs; and the Amur, 388,000 cfs. There are 250,000 lakes and 2,000,000 km2(775,000 mi2) of swamp areas. Potential energy of the rivers of the USSR is more than 400,000,000 kw, of which 80,000,000 kw are the share of the medium and small rivers. The total mean annual possible production is 2984 billion kw hrs. In 1957 the full capacity of all the reservoirs was 190 million acre‐feet, and the operational capacity was 120 million acre‐feet. The hydroelectric stations of the USSR account for about 20% of the total energy produced in the country. In 1955 the total length of the waterways was 132,000 km (82,000 mi.). The area of the irrigated lands was 11,100,000 hectares (27,400,000 acres or 42,800 sq mi), and the area of the reclaimed lands was 8,400,000 hectares (20,750,000 acres or 32,400 sq mi). Mean daily delivery of water through pipe conduits exceeded 4.7 billion gallons or 7300 cubic feet per second. These are impressive figures, especially taking into consideration location of the installations in a variety of climates under various natural con