NEW ORLEANS (AP) — Environmental advocates in states along the Mississippi River have won a round toward a long-term goal of having federal standards created to regulate farmland runoff and other pollution blamed for the oxygen-depleted “dead zone” in the Gulf of Mexico.

A federal judge in New Orleans did not order the Environmental Protection Agency to create standards. But he gave the agency six months to decide whether to set standards for nitrogen and phosphorus in all U.S. waterways or explain why they’re not needed.

EPA has said it could more effectively fight water pollution by working with states.

U.S. District Judge Jay Zainey ruled Friday that the U.S. Supreme Court’s 2007 ruling in a lawsuit about greenhouse gases and car emissions also requires EPA to investigate whether water pollution standards are needed.