Environmental and community groups have sued Utah officials over failures to save its iconic Great Salt Lake from irreversible collapse. The largest saltwater lake in the western hemisphere has been steadily shrinking, as more and more water has been diverted away from the lake to irrigate farmland, feed industry and water lawns. A megadrought across the US south-west, accelerated by global heating, has hastened the lake’s demise. Unless dire action is taken, the lake could decline beyond recognition within five years, a report published early this year warned, exposing a dusty lakebed laced with arsenic, mercury, lead and other toxic substances. The resulting toxic dustbowl would be “one of the worst environmental disasters in modern US history”, ecologist Ben Abbott of Brigham Young University told the Guardian earlier this year. Despite such warnings, officials have failed to take serious action, local groups said in their lawsuit, which was filed on Wednesday. “We are trying to avert disaster. We are trying to force the hand of state government to take serious action,” said Brian Moench of the Utah Physicians for a Healthy Environment, one of the groups suing state agencies. “Plaintiffs pray that this Court declare that the State of Utah has breached its trust duty to ensure water flows into the Great Salt Lake sufficient to maintain the Lake,” reads the lawsuit, which was brought by coalition that includes Earthjustice, the Utah Rivers Council, the Center for Biological Diversity and the Sierra Club, among others. Despite growing political momentum on the issue, scientists say the proposed measures are not nearly enough to save the lake, which has lost about 40bn gallons of water annually since 2020. The state’s Republican governor Spencer Cox has suspended new claims to water in the Great Salt Lake Basin and appointed a commissioner to oversee response to the lake crisis. Last year, Utah’s legislature passed several conservation measures, including a $40m trust to support lake preservation projects. But Abbot and his colleagues, who authored a sobering report on the lake in January, found that those measures increased flows to the lake by just 100,000 acre feet in 2022. About 2.5m acre-feet a year of water will need to flow into the lake to bring it to a healthy level, the researchers estimated. That water will likely have to come at the expense of agriculture, which takes in about three-quarters of the water diverted away from the lake to grow mostly alfalfa and hay. Cities and mineral extraction operations each take up another 9% of diverted water. But wresting water away from agriculture is politically complicated. Officials have explored propositions to pay farmers to fallow land and use less water, though such proposals have yet to gain much tractions. Lawmakers have also offered up a series of out-of-the-box solutions – including cloud seeding, which uses chemicals to prompt more precipitation – or building a giant pipeline from the Pacific Ocean. Emma Williams, a spokesperson for Cox, declined to comment on the lawsuit. Although historic winter snowfall has caused the lake to rise in recent months, perversely increasing the risk for violent runoff, scientists have warned that one wet year is not enough to reverse years of drought and water overuse. “The Great Salt Lake belongs to the people of Utah and the state has a legal obligation to protect this resource,” said Stu Gillespie, an attorney for Earthjustice’s Rocky Mountain office. “But the state has sidestepped that obligation and failed to respond to the crisis facing the lake.” Already, the lake has lost 73% of its water and 60% of its surface area, and is becoming saltier, threatening native flies and brine shrimp. A diminished lake may be unable to support the more than 10 million migratory birds that stop over in the region. A white pelican colony recently abandoned a nesting site on the lake, potentially due to declining water levels. “In addition to the millions of people who live here, so many plants and animals depend on the lake,” said Deeda Seed, Utah campaigner at the Center for Biological Diversity. “The health of northern Utah’s entire population depends on the Great Salt Lake’s survival and I hope this lawsuit can help save it.”