Shipwrecks have become visible under Lake Michigan as ice melts from the surface of the water. Normally hidden under the murky waters of the massive marine body, the remains of several vessels are showing through the unusually clear water.

The ships date from the 19th and 20th centuries, and were first seen by observers flying above the lake in a helicopter. Photographs were taken on April 17, and first released on Facebook by the U.S. Coast Guard. The crew was on a routine patrol when members spotted the shipwrecks.

"During a routine patrol this past Friday, an aircrew captured these photos of a handful of the many shipwrecks along the Lake Michigan shoreline. These photos were taken near Sleeping Bear Point northeast along the shoreline to Leland, Mich., up to Northport," the U.S. Coast Guard Air Station in Traverse City reported on its Facebook page.

The Rising Sun, a steamer ship which sank in 1917, was one of the ships which became visible under the lake.

"This 133-foot-long wooden steamer stranded just north of Pyramid Point. She went to pieces and her wreckage now rests in 6 to 12 feet of water," Coast Guard officials reported.

The James McBride, a cargo ship which gained notoriety in the 19th century as the first brig to deliver cargo directly from the Atlantic Ocean to a port in Lake Michigan, was another of the vessels spotted by the Coast Guard crew. This craft struck ground near Sleeping Bear Dune in 1857 during extreme wind conditions, sinking 5 feet beneath the water.

Changing environmental conditions periodically reveal and hide shipwrecks under the lake, allowing observers to view ships beneath the waters. One of the ships seen from time to time, the schooner the Jennie & Annie, sunk beneath the surface of the water in 1872. It is periodically visible from the beach halfway between North and South Bar lakes. 

The Manitou Passage Underwater Preserve, where many of the shipwrecks were spotted, is heavily-trafficked by commercial shipping, and is known for wrecks of freighters. It surrounds North and South Manitou Islands in Lake Michigan and is next to Michigan's Sleeping Bear Dunes National Lakeshore.

Lake Michigan stretches over nearly 22,400 square miles, making it the second-largest of the bodies in the Great Lakes system. It is the only one of the five lakes to be located entirely within the United States. The other four water bodies in the system border both the United States and Canada. The nation's third-largest city, Chicago, sits on the massive water body, along with the states of Illinois, Indiana, Michigan and Wisconsin.

These shipwrecks are legally considered to be public property, protecting the artifacts from being plundered. However, some of the wrecks can still be explored by divers.

The remains of World War II-era ship the USS Independence were recently shown off the coast of California in the Farallon Islands, where it was seen in 3D images taken by a submersible to be in good condition, an airplane visible on its flight deck, in 2,600 feet of water.