Okjeongho Lake is located in Janggeum-ri and Jonsung-ri in Sannae-myeon, Jeongeup-si, and its water is from Seomjingang River Dam. The left and right of tributary of the dam are Ganjin-myeon, Imsil-gun and Sannae-myeon, Jeugeup-si. The former dam was constructed from November 1st, 1925 to December 1927, and the new dam was constructed from April 1940 to December 1965. Okjeongho Lake was formed during the construction of Unam Reservoir in 1928 in order to supply agricultural water to Honam Plain region. The Unam Reservoir was rebuilt in 1965 as the Seomjingang River Dam to expend its water capacity and for power production purposes, and Okjeongho Lake was widened with the construction of the dam. The lake used to be called and marked as Unamho Lake, or Seomjinho Lake but, now it is called Okjeongho Lake.