The federal government refuses to recognize the declaration, standing by a 1960 U.S. Supreme Court decision that determined the offshore boundary for Mississippi, Louisiana and Alabama was three miles out.
The federal government also has not recognized Louisiana's 2011 declaration of a nine-mile limit.
At stake is Gulf states' control of lucrative fishing rights and revenue from oil and gas production in near-offshore waters.
Mississippi's congressional delegation has been seeking to force federal recognition of the nine-mile limit for recreational fisheries management. Republican Sen. Thad Cochran proposed an amendment that would do so through a wide-ranging bill that focuses on hunting, fishing and outdoor recreation policy.
The issue dates back to 1953, when Congress passed the Submerged Lands Act. The act established a coastal boundary for each state at three geographical miles from the shore. The federal government retained control of water bottoms farther out.
The act provided that Congress could vote to extend the boundaries up to 10 miles offshore if a state could prove the existence of a law or constitutional provision that established a boundary beyond three miles before that state joined the Union.
In a 1960 lawsuit brought by the federal government, the five Gulf states argued each qualified for an exception. The U.S. Supreme Court decided Texas and Florida had produced historical documents supporting a 10-mile boundary but it ruled Mississippi, Alabama and Louisiana did not.
After 30 more years of litigation, the government, the Supreme Court and the states in 1992 set a legal definition of where each of the three states' coastline began — and from there the three-mile limit would be determined. The decree did not extend the three-mile limit.
Louisiana wildlife officials said the state Legislature gave authority to extend waters in 2011 — but only after it was recognized by Congress or approved in litigation.
The Mississippi law of 2013 mimics the Louisiana law, but without the reference to Congress.
Its author, Rep. Casey Eure, R-Biloxi, said at the time that the bill was important to recreational and commercial fishermen. Eure said Louisiana's plan would overlap some waters where Mississippi officials had placed reefs and where Mississippi recreational and commercial fishermen had harvested for years. It was unclear how the two states would work out the overlap matter.
Cochran said his proposal also would assert state authority for managing, leasing, developing and using recreational fisheries within the extended area.
"Recreational fishing in the Gulf of Mexico is an important part of the economy and lifestyle of south Mississippi. The federal government not recognizing Mississippi's right to extend its waters for the purpose of fishing adversely affects these activities, as we saw this year with the shortened red snapper season," Cochran said.
The federal red snapper season ran June 1-9. Most of the red snapper fishing is in the deeper federal waters near oil rigs. But the Mississippi Department of Marine Resources decided the nine miles of waters would be open for red snapper fishing through much of July.
The agency told fishermen the federal government does not recognize this distance, and anyone possessing red snapper farther than three miles south of the barrier islands could be cited by federal law enforcement officers. Officials said fishing between three and nine miles in Mississippi waters is at the angler's own risk.
Cochran said his proposed amendment would have remedied the problem.
(Daily Corinthian columnist Jack Elliott Jr. covers Mississippi politics and legal affairs for The Associated Press based in Jackson.)