The Hoover Dam is the most famous such example in North America, and for good reason. Built between 1931 and 1936 during the Great Depression, the project was truly a feat of engineering for the time.

Standing 726 feet high, and 1,244 feet long, the dam—in the Black Canyon of the Colorado River—is certainly impressive. It also forms Lake Mead, the largest manmade reservoir in North America. The lake has gained national attention recently because of its rapidly declining water levels.

The Hoover is now the most visited dam in the world, and draws 7 million tourists a year.

A photo shows Hoover Dam, in Nevada and Arizona, at dawn. The structure was originally built in the 1930s for flood control. Sean Pavone/Getty

Robert Glennon, a water policy and law expert and emeritus professor at the University of Arizona, told Newsweek: "Building a dam at this scale had never been done [at the time of construction]. It was an engineering marvel."

However, it is a lot more than just a tourist attraction, and the southwest U.S. exists, as we know it today, because of the Hoover Dam.

Why Was the Hoover Dam Built?

There were three main reasons for the construction of the dam, and the first, most vital one, was flood control.

Before the dam was constructed, the Colorado River flowed wildly and untamed through the Rocky Mountains, all the way south to the Gulf of California, for 1,450 miles. The river, supplied by snowpack coming down from the mountains, would regularly flood the surrounding regions, depending on how full it was that year.

"The Colorado River was wildly up and down, depending on snow melt in the Colorado Rockies. It could be a big year or a low year—and they were trying to even that out," Glennon said.

"Because a lot of the best lands in the Lower Colorado are adjacent to the river itself. So it got a huge flood. In fact, the Bureau of Reclamation said the river was, quote, 'a natural menace.'"

One such example of this flooding occurred between 1905 and 1907, when the Colorado River broke through its banks and flooded 100,000 acres of farmland in Southern California. This was around the same time that the Bureau of Reclamation started planning for a dam in the Boulder Canyon region, on the Colorado River.

Plans were set in motion, but flood control was not the only thing they had to think about. Water supply was another main reason for building the Hoover Dam.

"The second very important purpose [for its construction] was water supply. About 40 million people depend on water from the Colorado River, and that is through Hoover Dam. Once it was constructed, the river flowed when the Bureau of Reclamation determined it would flow," Glennon said.

Before the Hoover Dam, farmers downstream had a lot of water only in the spring when the snowpack melted. Then the water would peter out by the end of the summer.

However, with the construction of the dam, the flow could be controlled, meaning farmers had access to water 365 days a year.

"And that was just an enormous game-changer," Glennon said. "[...] This water supply being evened out over the whole year, gave farmers a tremendous opportunity to plant more than one crop during the year."

Lastly, the Hoover Dam was built for power. Although this was not as vital as preventing flooding, or providing irrigation, it is a function of the dam that continues to this day.

"They attached some turbines and all of the high-wire lines to move the electricity created at Hoover Dam, and that's just simply a function of having built the dam in Boulder Canyon," Glennon said.

"The water that was held back in Lake Mead, when the lake was full, there would be a drop of 500 or 600 feet—a very big drop. And all of that is potential energy," Glennon added. "So, spinning the turbines generated hydropower."

To this day, Hoover Dam produces about 4 billion kilowatt-hours of hydroelectric power every year for about 1.3 million people living across Nevada, Arizona and California.

Why Is Lake Mead Drying Up?

The Hoover Dam relies on water from Lake Mead to function, but the reservoir has seen better days.

Lake Mead is drying up because of the ongoing megadrought in the southwestern U.S, paired with the overconsumption of water in the region.

The drought is making weather patterns—such as seasonal rainfall—harder to predict, and less frequent. This has meant water is being used faster than the lake can replenish itself.

The Colorado River also relies on snowpack from the Rocky Mountains for water, and this is also becoming harder to predict.

Some parts of the U.S. saw a colder winter than usual, meaning the snowpack is better in 2023, when compared to previous years in the drought.

This may make water levels rise temporarily, but as the drought has gone on for so long, it will be short-lived. It would take years of increased rainfall and cooler temperatures to lift the drought.

Will Lake Mead Reach Dead Pool?

It is feared that Lake Mead could reach dead pool, if water levels continue declining at the rate they are.

Dead pool would mean that Lake Mead's water levels got so low that water would no longer flow past Hoover Dam, making it unfunctional for irrigation and electricity.

As of February 14, Lake Mead's water levels stood at 1,047.51 feet. It is just less than 30 percent full, and dead pool would be at around 895 feet. The Bureau of Reclamation predicts that Lake Mead, if it continues drying up at the same pace, could reach dead pool by 2025. In July 2022, the lake reached its lowest-ever point at 1,040 feet.

Now, officials are working to figure out a plan to prevent dead pool from happening. Because if it did, it would be a "catastrophe" for the surrounding region, Glennon said.

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