U.S. Sen. Johnny Isakson has cut short a study of whether the federal government should crack down on pollution of the Ogeechee River.
Isakson spokeswoman Lauren Culbertson said Senate ethics rules bar members from intervening in matters that are "in the adjudicative process."
An estimated 38,000 fish died in the river last year. Some blame industry along the river for the deaths.
The Georgia Environmental Protection Division discovered an unpermitted wastewater discharge from the King America Finishing facility in Screven County during an investigation into the major fish kill in May 2011.
The agency and King America Finishing reached a settlement in which the company agreed to spend $1 million on environmental projects to benefit the Ogeechee.