U.S. EPA has delayed guidelines aimed at curbing discharges of polluted water from power plants, environmental groups that sued the agency over the rule said yesterday.

The groups -- Defenders of Wildlife, Earthjustice, the Environmental Integrity Project and the Sierra Club -- filed a joint motion in federal court this week allowing EPA to delay release of new rules to April 2013 that had been set for this Friday.

"Ensuring the EPA provides the strongest guidelines possible for toxic wastewater from power plants is an important step in protecting American families and ensuring our water is safe to drink," EIP managing attorney Jennifer Peterson said in a statement. "Although EPA insisted on this last delay, families across the country can't wait much longer for clean water."

The groups sued EPA in 2010, accusing the agency of failing to update decades-old rules as the Clean Water Act requires.

EPA agreed quickly to settle. This week the agency said it had no plans to seek further delays of initial rulemaking and would release final rules by 2014.

An industry group -- the Utility Water Act Group -- had its effort to intervene in the case denied by U.S. District Court for the District of Columbia Judge Richard Roberts.

The group is appealing Roberts' decision and is questioning the environmental groups' assertion that EPA is legally bound to issue new rules.

"If Plaintiffs are correct that the law imposes this non-discretionary duty on EPA, and the facts alleged demonstrate that EPA has failed to perform it by some statutory deadline," the group wrote in court papers, "the consequences for UWAG's members would be concrete and particularized, immediate, and causally related to this lawsuit."

EPA said it is pursuing the rulemaking largely because of discharges from coal-fired power plants that are expected to increase with technology to limit air emissions.

"The primary routes by which coal combustion wastewater impacts the environment are through discharges to surface waters, leaching to ground water, and by surface impoundments and constructed wetlands acting as attractive nuisances that increase wildlife exposure to the pollutants contained in the systems," EPA said in a 2009 report.

"EPA found the interaction of coal combustion wastewaters with the environment has caused a wide range of environmental effects to aquatic life."