The Hoover Dam, a massive structure spanning the Colorado River at the border of Nevada and Arizona, was built with a unique method to ensure its strength and durability. During its construction, a refrigeration plant was installed near the site, capable of producing the equivalent of 1,000 tons of ice every 24 hours. This ice was used to cool the concrete as it was poured, helping it harden properly. The dam, which holds back the waters of Lake Mead—the largest reservoir in the United States—was designed to provide water to 18 million people in Arizona, Nevada, and California, as well as to irrigate over one million acres of farmland. The construction of the dam required an enormous amount of concrete, totaling 3,250,000 cubic yards. Without proper cooling, the heat generated by the chemical reaction of the concrete could have caused internal stresses and eventual cracking. To prevent this, engineers from the Bureau of Reclamation divided the dam into separate columns, each poured in blocks. These blocks were constructed in lifts, with some reaching up to 15 meters in height. Inside each block, a network of steel pipes was embedded to circulate water and cool the concrete. Initially, water from the Colorado River was used to begin the cooling process, and later, colder water from the refrigeration plant took over. The refrigeration plant, one of the largest of its time, was built on the lower part of the river. Once a block had cooled sufficiently, its pipes were sealed with grout under high pressure. The blocks were also designed with interlocking grooves, like puzzle pieces, to ensure a tight fit. After each block had cooled, cement grout was injected into the spaces between columns to bond them together. The dam was completed on March 1, 1936, more than two years ahead of schedule. Although some legends suggest the concrete is still hardening today, the majority of the structure has long been fully set. Some of the original cooling pipes are still visible on guided tours of the dam, more than 90 years after they were installed. This innovative approach to cooling and construction played a crucial role in the dam's enduring strength and stability.