Environmental organizations have filed a lawsuit in California in a bid to stop oil drilling waste injection wells threatening the state's dwindling groundwater supplies.

The lawsuit, filed by Earthjustice on behalf of the Center for Biological Diversity and Sierra Club, challenges new "underground injection control" regulations introduced by California's Division of Oil, Gas and Geothermal Resources (DOGGR).

The organizations claim that these rules allow oil companies to continue injecting oil industry wastewater and other fluids into protected aquifers until February 2017. This, they say, is in violation of state and federal law and comes despite a water-scarcity crisis caused by California's worst drought on record.

Earthjustice asked the court to declare the new regulations illegal and force California officials to immediately end such injection operations, which activists believe are contaminating underground water in scores of aquifers across the state.

"Instead of halting the operations of these underground injection wells, these regulations allow DOGGR to delay shutting down illegal operations for nearly two more years," commented Earthjustice Staff Attorney Will Rostov, adding that officials had re-written the law "to allow needless and unlawful contamination of drinking water during a severe drought for the benefit of the oil industry."

"It's inexcusable that state regulators are letting oil companies dump toxic wastewater into California's water supplies during the worst drought in 1,200 years," agreed Hollin Kretzmann, a staff attorney for the Center for Biological Diversity. "The oil industry's illegal injections need to stop immediately to protect our groundwater."

Last year, a review found that more than 2,500 underground injection wells in California had been permitted into aquifers that were supposed to be protected as current or potential sources of water for drinking and agricultural use.

An emergency order issued by DOGGR in April set out a timeline for oil companies to stop injecting into certain wells. Regulators also ordered the immediate shutdown of 23 injection wells and launched a review of others to determine their impact on water supplies.