Lake Mead, the reservoir formed by the Hoover Dam on the Colorado River in southern Nevada, hit its lowest water level on record this week. It’s a symptom of the “megadrought” gripping the Western United States, depleting water resources and contributing to record wildfire seasons.

Water levels in the lake have been in steady decline since the early 2000s, briefly improving around 2012 before dwindling again. Now water levels are more than 140 feet below what the U.S. Bureau of Reclamation defines as “full.”

The disconcerting water-level record comes ahead of a week of extreme temperatures that will climb to near 110 degrees. The area surrounding Lake Mead, the largest reservoir in the United States, is under an excessive heat warning.

It’s possible that, in years ahead, the Hoover Dam may no longer be able to generate electricity at certain times of the year as a result of subsiding water levels.

At top capacity, Lake Mead’s water would come to an elevation of 1,229 feet, but it is considered full when maximum water elevation reaches 1,219.6 feet. Lake levels reached an all-time minimum of 1,071.44 feet on Thursday, below the previous record low set July 1, 2016.

The lake began filling in 1934 before the Hoover Dam’s completion in March 1936. Since then lake levels have been monitored continuously, and are a product of river inflow, controlled release, precipitation and evaporation. When the lake is full it covers 248 square miles. The release is used to generate electricity and supply water demand in the area, including to farms and communities, including Las Vegas. The city receives roughly 90 percent of its drinking water from the lake.

During most of the 1980s and ′90s, water levels hovered around 1,200 feet, with minimal year to year variation. Then levels began to decline around the year 2000. The lake hasn’t hit 1,150 feet since April 2003, and April 2014 was the last time water levels stood at 1,100 feet.

The Colorado River, which feeds Lake Mead, has an extensive watershed that covers 246,000 square miles and occupies seven states. Precipitation that falls as far north as southwestern Wyoming or into the Rockies of western Colorado or northwestern New Mexico can eventually make it into the river, ultimately entering Lake Mead. That makes Lake Mead a sort indicator for the entire West.

Right now the West is struggling amid a drought that has reached crisis levels in some spots. According to the U.S. Drought Monitor, 55 percent of the West is dealing with “extreme” or “exceptional” drought, the two most severe categories. The highest-tier drought category engulfs most of southern Nevada and adjacent Utah.

Utah’s governor has resorted to soliciting collective prayers from residents of the state in hopes of “divine intervention.”

The drought has been made worse by anomalously hot temperatures intensified by human-induced climate change that continues to bake the region every summer. Hotter temperatures lead to greater direct evaporation and evapotranspiration, or evaporation from plants. That saps the ground and vegetation of water more effectively, drying out the landscape and leaving it a powder keg for rampant wildfire growth during the autumn.

Drier landscapes also favor high temperatures, which in turn reinforces the drought in a vicious self-perpetuating process.

Mother Nature shows no signs of offering any aid to the situation, instead exacerbating it as a sprawling heat dome settles over the Four Corners region and brings near-record temperatures next week. High temperatures over Lake Mead could approach 110 degrees, with the Weather Service warning that “extreme heat will significantly increase the potential for heat-related illnesses, particularly for those working or participating in outdoor activities.”

Looking ahead, a forecast bull’s eye of anomalous warmth will linger through the remainder of the summer, further worsening the already severe drought and depleting lake levels even more.

Historically, the Hoover Dam required water levels exceeding 1,050 feet to generate electricity, but engineers, knowing there will probably be a day in the not-so-distant future when that threshold can’t be reached, made turbine modifications that can produce some electricity with as little as 950 feet.