The Thunder Bay National Marine Sanctuary in northern Michigan has received federal approval to expand its size nearly tenfold and boost the preservation of scores of sunken vessels in an area of Lake Huron once known as “Shipwreck Alley”.

Thunder Bay, the only freshwater national sanctuary, is announcing on Friday that the Obama administration has approved the years-in-the-making effort to grow from about 450 square miles to 4,300 square miles. The expansion — which incorporates the waters from off Alcona, Alpena and Presque Isle in the north-eastern Lower Peninsula and to the maritime border with Canada — also doubles the number of estimated shipwrecks to roughly 200.

The effort to expand the sanctuary, originally created in 2000, started with three failed congressional bids and then the administrative review process through the Commerce Department. The department oversees the National Oceanic and Atmospheric Administration, which manages the sanctuary along with the state of Michigan.

“It’s been a long, long effort,” the sanctuary superintendent, Jeff Gray, said. “It’s a pretty monumental thing ... In a small way we raise the Great Lakes into this national dialogue.”

While many spots along the Great Lakes are hazardous, Thunder Bay became known as “Shipwreck Alley” in the 19th century, as it was part of a major shipping channel during an era when the region had few alternatives.

The sanctuary was established to protect cultural resources and focuses on shipwrecks, but its research often finds dual uses. For instance, the systematic mapping of the lake bottom has helped to identify the wrecks and provide scientific data — such as fish-spawning areas — to share with fisheries biologists.

Still, the wrecks remain the main attraction. Among the better known is the Isaac M. Scott, a propeller-driven coal carrier that fell victim to the Great Storm of 1913, which scuttled 11 vessels in 16 hours and killed 150 mariners. Another is the New Orleans, a wooden side-wheeler that hit a reef on a fogbound night in 1849. All 300 passengers and sailors were rescued.

Expanding the sanctuary’s boundaries also fosters further exploration and the possibility of locating other vessels.

“It’s really the timeline of Great Lakes shipping down there,” Gray said. Vessels are found at all depths — some are accessible by kayak or glass-bottom boat, others can be explored by snorkellers and recreational divers, while the deepest are accessible only to technical, professional diving crews.

Gray said the sanctuary has worked over the years to iron out concerns and criticisms, such as divers fearing blocked access, but sanctuary officials have encouraged them to visit by placing buoys on sites. Officials also worked with the shipping industry, which led to excluding the waters in three area ports, as well as regional Indian tribes to ensure that the expansion would not affect treaty fishing rights.

The sanctuary draws about 80,000 visitors annually, and Gray said they hope to hit 100,000 this year.