The nation's only freshwater sanctuary has been given the federal go-ahead to grow nearly 10 times its current size and expand efforts to preserve sunken vessels in an area of Lake Huron known as "Shipwreck Alley."

Thunder Bay National Marine Sanctuary announced Friday the Obama administration's approval of a plan to increase its boundaries from 450 to 4,300 square miles, which includes waters off of Alcona, Alpena and Presque Isle in the northeastern portion of Michigan's Lower Peninsula, up to the maritime border with Canada, reports the Associated Press.

The decision also doubles the estimated number of shipwrecks in the sanctuary's care to about 200.

The push to expand the sanctuary follows three failed Congressional bids to add to the area's perimeter, followed by a lengthy administrative review process through the Commerce Department, which oversees the National Oceanic and Atmospheric Administration, that in turn manages the sanctuary in cooperation with state of Michigan.

"It's been a long, long effort," sanctuary superintendent Jeff Gray said in the AP article. "It's a pretty monumental thing. ... In a small way we raise the Great Lakes into this national dialogue."

The sanctuary was established in 2000 to protect cultural resources, particularly the historical shipwrecks.

The systematic mapping of the lake bottom over the years has aided in the identification of wrecks, but has also yielded scientific data -- such as fish-spawning areas -- shared with fisheries biologists.

The wrecks, however, are the area's main attraction.

While many spots along the Great Lakes are hazardous, Thunder Bay, part of a major shipping channel during an era when the region had few navigational options, became known during the 19th century as "Shipwreck Alley."

The better known wrecks include the Isaac M. Scott, a propeller-driven coal carrier lost to the Great Storm of 1913, which in total sank 11 vessels in 16 hours and killed 150 mariners.

Another notable wreck is that of the New Orleans, a wooden side-wheeler that ran into a reef during thick fog in 1849. All 300 passengers and sailors were rescued in that accident.

Gray explained vessels are found at all depths in the sanctuary, with some easily accessible by kayak or glass-bottom boat.

Others are open to be explored by snorkelers and recreational divers, while the deepest are limited only to professional diving crews.

The sanctuary pulls in about 80,000 visitors annually, though Gray hopes to draw at least 100,000 this year.

"It's really the time line of Great Lakes shipping down there," he said.