The Chesapeake Bay Foundation is challenging a Virginia State Water Control Board decision that allows Merck & Co. to increase its pollution discharge into the Shenandoah River.

The state board in April approved the pharmaceutical giant's request for its Elkton plant to discharge an additional 29,216 pounds of nitrogen and 3,288 additional pounds of phosphorus annually into the river's South Fork. The amounts are beyond the emissions limits Virginia established in 2005 as part of a multi-state effort to clean up the Chesapeake Bay.

The environmental group and the Virginia State Waterman's Association filed a lawsuit Monday asking the Richmond Circuit Court to set aside the new discharge limits and send the issue back to the water board for reconsideration. It argues that allowing Merck to discharge more pollutants violates the overall nutrient cap for the Shenandoah-Potomac River basin and ultimately harms the bay.