The Nanni swamp supplies irrigation water for about 18,000 ha of agricultural lands, mostly for the rice culture. The total area of the swamp is about 1,550 km². The only source of water available for the swamp is the rainfall and the inflow from the Zanderij formation and the Old coastal plain. A water balance shows that in a year with average rainfall the discharge is 12.5 m³/s.  In an extreme wet year discharge increases to 16.8 m³/s., and in an extreme dry year the discharge falls up to 9.5 m³/s. The total area of the Coronie swamp is about 70,000 ha. The area of the Coesewijne swamp depends on its water level. During the rainy season it may extend over 800-900 km². The man-made lake, the Prof. Dr. Ir. Van Blommenstein reservoir, is the largest artificial open freshwater resource in Suriname. It is located in the Suriname river at Afobaka, 194 km upriver. It covers an area of 1,560 km². The purpose of this reservoir is to provide electricity for the aluminum smelter at Paranam (operational in 1964). Controlled discharge at Brokopondo provides a mean yearly flow of approximately 250 m³/s.