After that, in 1934, the bottom part of the bottle-gourd-shaped Naganuma (front marsh) was reclaimed under the reclamation project, and in 1942, the upper part of the marsh (back marsh) was reclaimed under the national increase food production project, the construction was completed in 1953, gathering 1000 members of Volunteer Pioneer Youth Army of Manchuria and Mongolia and 1000 local people for the construction of drainage ditch,.
その後、長沼は昭和9年、ひょうたん型の下の部分（前沼）が干拓事業により干拓され、後の昭和17年、沼の上の部分（後沼）が国の食料増産事業により干拓が行われ、排水路工事には満蒙開拓青少年義勇軍1000人と地元民1000人が招集され、昭和28年完工した。