The Ik-ok Irrigation Association was a large association established with an irrigated area of 9,460 『jeongbo』 (approximately 23,183 acres) and around 2,000 members along the middle and lower sections of the Mangyeonggang. The association merged the Southern Im-ik Irrigation Association and the Im-ok Irrigation Association, both of which were limited by a lack of water supplies in their respective districts. Furthermore, water inputs to these areas was decreasing year on year as the upper regions of the river were reclaimed. Based on this, Fujii Kantaro, the “King of Korean Irrigation”, devised a plan to merge the two irrigation associations and construct a mega-dam in the upper region of Gosancheon to secure water supplies.
Construction of the Dae-a Reservoir dam was called the “Korea’s biggest construction project”. It began in February, 1920, and was scheduled for completion within 2 years. But it was only completed three years and four months later, in June, 1923. The initial construction budget was 2,360,000 won, increasing to more than 3,900,000 won as the construction period was extended with an additional cost of about 500,000 won in land purchases. Thus, the Ik-ok Irrigation Association issued 4,400,000 won of bonds which increased the burden of membership fees on association members.