Parts of California’s central valley are sinking, the Sacramento Bee reports, as farmers faced with drought and water sources cut off to protect the Delta smelt are pumping out deep groundwater to save their crops. The situation is serious enough that even some farmers are calling for new regulations on groundwater usage.

It’s called subsidence, and it happens when farmers desperate for water dig deep wells into clay aquifers. As the water is pumped out the press of earth above compresses the clay. The land sinks and the compressed clay can not hold as much water as it once did. Once subsidence happens there is no way to undo it.

Michelle Sneed, who studies subsidence for the U.S. Geological Survey, authored a study in 2013 which found that 1,200 square miles of the Central Valley were sinking half-an-inch per year. But the rate is not consistent everywhere. The town of El Nido, CA just south of Merced sank almost a foot a year between 2008 and 2010. “A foot a year is not sustainable. You can’t really mitigate against a foot a year,” Sneed told the Bee.

Sneed’s job is made more difficult by the fact that the state does not collect information on the amount of water being pumped out of California’s deep aquifers. Counties do approve wells but do not monitor them. 

Tim Parker of the Groundwater Resources Association of California (GRAC), an associations of scientists in the field, told the Bee: “You have to require that these big pumpers measure and report to the local agencies.”

One big factor impacting the subsidence issue in the Central Valley is the battle over water from the Sacramento River which, starting in 1933, was diverted to the area as part of the Central Valley Project. Much of that water has been cut off in recent years as the result of a lengthy legal battle over the Sacramento-San Joaquin Delta and in particular a small fish called the Delta smelt.

Three years of below average rainfall have made the drought in the Central Valley a critical issue. President Obama visited the area in February to announce $170 million in aid. However, the President said he would not “wade into” the battle over water rights in the state, joking that he wanted to “get out alive on Valentine’s Day.”

In the short term farmers can dig more wells and draw more water from underground aquifers to keep their crops growing, but in the long term this creates subsidence and insures that those aquifers will not refill in the future.