Four underground tunnels were built to move water around the dam from Fort Peck Reservoir to the Missouri downstream. On June 24, 1937, the dike holding back the Missouri River was blasted with dynamite, and since then the river has flowed through these tunnels. The only other way water can be released from the reservoir is when the lake becomes high enough to discharge water through the spillway. About 4,000 men worked day and night for nearly four years to build the tunnels. Their construction required 117 million pounds of steel, 660,000 cubic yards of concrete, and the removal of nearly 4 million cubic yards of material, enough to fill 500,000 dump trucks. Each tunnel was designed to safely carry the entire flow of the Missouri River on its own. Today, two of the tunnels feed water to the powerhouses, while the other two are reserved for bypass flows if needed.