Environmental groups have filed a pair of lawsuits in federal district courts to force the U.S. Environmental Protection Agency to take tougher action to curb pollutants in the nation’s waterways.

The Natural Resources Defense Council and other environmental organizations say their lawsuits, filed March 13,  are necessary to reduce the size of large algae blooms, or “dead zones,” that stretch for miles in the Gulf of Mexico, Chesapeake Bay and other waterways across the nation.

But the National Association of Clean Water Agencies (NACWA) says a court ruling in the environmental groups' favor could have “astronomical” financial implications for wastewater-treatment agencies, which would need to upgrade their facilities to comply with stringent new standards.

One of the lawsuits challenges a 2011 EPA decision to leave the responsibility for setting numeric limits for nitrogen and phosphorus to the states, instead of issuing a nationwide federal standard for states that had not developed such benchmarks.

The other lawsuit seeks to direct EPA to respond to a 2007 petition the organizations submitted, which requested that the agency add nutrient removal to current Clean Water Act secondary-treatment requirements.

Ken Kirk, NACWA executive director, said in a statement: “NRDC and the environmental community know full well that simply forcing wastewater-treatment plants to install costly treatment upgrades will not solve the nutrient pollution problem but will just lead to higher rates for already cash-strapped ratepayers and local governments.”

Kirk added, “Costly litigation that seeks to impose stringent, costly and one-size-fits all controls on ratepayers nationwide is simply a waste of resources and perpetuates the myth that this strategy will be effective in addressing nutrient pollution—it won’t.”

According to NACWA, a technology-based treatment limit for every U.S. wastewater-treatment plant could cost more than $280 billion in initial capital expenses.

But the environmental groups argue that a ruling in their favor would compel EPA to exercise its responsibilities under the Clean Water Act to work toward reducing what NRDC calls a “pernicious” environmental concern.

One lawsuit was filed in U.S. District Court for the Southern District of New York; the other was filed in U.S. District Court for the Eastern District of Louisiana.