Poultry companies began their defense against a federal pollution lawsuit with a water quality expert who testified that wastewater treatment plants are the major culprit in phosphorus pollution, according to Tulsa World.

The testimony was part of an ongoing lawsuit brought against 11 poultry companies by Oklahoma Attorney General Drew Edmondson. Oklahoma contends that runoff from poultry litter has degraded the Illinois River watershed and seeks a ruling that would end its use as fertilizer.

The defense’s water quality expert, John Connolly, testified shortly before Christmas that poultry litter contributes a negligible amount of phosphorous to the Illinois River watershed and that wastewater treatment plants in the area are responsible for 80% of the phosphorous that leads to algae bloom.

Earlier, witnesses for the state testified that chicken litter has 3.5 to 6 times the phosphorous levels of cow manure and has been identified in the sediment of Oklahoma’s Lake Tenkiller, according to Tulsa World.

Oklahoma has worked on the lawsuit since 2004 and private law firms have completed an estimated $25M worth of work on the state’s case, reported Tulsa World.

Frizzell dealt a blow to the state’s case on Dec. 15 when he ruled that chicken litter used as fertilizer does not qualify as solid waste under the federal Resource Conservation and Recovery Act. Edmondson refocused his arguments to whether chicken companies’ alleged water pollution violates trespassing laws and national and state nuisance laws.