To fix the Colorado River’s constant water problems, environmental groups want the Trump administration to use the federal government’s power to stop people from wasting water.

The Natural Resources Defence Council and nine other groups sent a petition to the U.S. Bureau of Reclamation on Tuesday asking them to follow a rule in federal rules that says water deliveries in California, Arizona, and Nevada “will not exceed those reasonably required for beneficial use.”

The petition is mostly directed at wasteful water use in farmland, which is responsible for about three-quarters of the water that is taken from the Colorado River, according to Mark Gold, who is in charge of water scarcity solutions for the council.

“There is definitely a great deal of room for improvement in the agricultural sector,” he said. He said that flood-irrigating desert farm areas all year to grow crops that need a lot of water, like hay, was an example of waste.

Hays like lucerne and others are fed to cattle and other animals, and more and more of them are being sent to China, Saudi Arabia, and other places these days.

Leaders of the environmental groups wrote in the petition, “Exporting these crops that need a lot of water is the same as exporting water itself, which is an urgently needed resource in the United States.” It was also said that a lot of the farmland in Southern California that gets its water from the Colorado River is “either fully or partially irrigated via flood irrigation, which uses a lot more water than drip and sprinkler irrigation.”

Farmers and officials of agricultural water agencies, like the Imperial Irrigation District in California, have taken part in programs that save water. If growers are paid enough to help pay for it, they are willing to switch to irrigation systems that use less water. This will free up water and raise the level of reservoirs.

But people who work in farmland have also said that in many places they have water rights that go back more than a hundred years. This means that they should be given more water and less water should be cut back. A lot of farmers have also said they are against plans where the government tries to tell them what foods to grow.

The petition was sent by leaders of several groups, including Los Angeles Waterkeeper, Orange County Coastkeeper, and the Utah Rivers Council. It asked the government to also look into how towns and businesses waste water.

They said that towns water grass that is only there for looks and that “outdated evaporative cooling systems cause inefficient industrial processes that use more water than needed.”

Thirty Native American tribes and farming communities from the Rocky Mountains to northern Mexico get their water from the Colorado River. Cities from Denver to Los Angeles also use it.

Gold said that the “beneficial use” clause was “a very important tool in making sure that the Colorado River and the 40 million people who depend on it have a sustainable future.”

He said, “The Bureau of Reclamation has the power and duty to stop the waste and protect this valuable resource.”

The river has been used too much for a long time, and since 2000, the reservoirs have dropped greatly because it has been dry. Since 2000, the river’s normal flow has dropped by about 20%. Scientists think that burning fossil fuels has caused about half of that drop.

Lake Mead and Lake Powell, the river’s two biggest reservoirs, are both 33% full.

More and more people are pushing the seven states that depend on the river to talk about new rules for how to handle shortages after 2026, when the current rules run out. The talks haven’t gone anywhere, though, because the four states in the river’s upper basin—Colorado, Utah, Wyoming, and New Mexico—and the three states in the river’s lower basin—Arizona, Nevada, and California—remain disagreeing.

Some water managers and experts have said that the federal government should make sure that people use less water by defining what “beneficial” use of water means and what “unreasonable” use of water means. It is thought that the environmental groups’ legal petition is the first attempt to force government officials to use their power in this way.

The environmental groups said in the petition that “climate change is causing the Colorado River’s water levels to drop, and this trend is expected to continue and get worse.” They also said that “the growing disparity between supply and demand will lead to a severe crisis” if the federal government doesn’t change how it delivers water in California, Arizona, and Nevada, where the rules apply.

A lot of the water in the Colorado River is used for farming. In a study released last year, researchers found that alfalfa and other cattle-feed crops consume 46% of the water that is diverted from the river, accounting for nearly two-thirds of agricultural water use. The study also found that farmland takes 74% of the water that is diverted from the Colorado River, making it the biggest user of the water.

Part 417 of the federal regulations is at the centre of the petition. It says that the Bureau of Reclamation has to make sure that the amount of water it sends to the three lower basin states “will not exceed those reasonably required for beneficial use.”

A message from Cara Horowitz, head of UCLA’s Frank G. Wells Environmental Law Clinic, which is representing the groups, said, “Our findings are that the Bureau is not adhering to this requirement.”

“We hope the Bureau will see the urgency of improving its water delivery process to avoid wasting Colorado River water, especially given how constrained our supply is,” Horowitz said. “But if it doesn’t, we’re ready to think about what to do next, which could include going to court.”