(AP) — The clear blue, post-winter waters of northern Lake Michigan have disclosed some of their hidden history to a U.S. Coast Guard crew, which took a series of photographs of shipwrecks lying on the lake bottom in the waters off the Sleeping Bear Dunes National Lakeshore. The Grand Rapids Press (http://bit.ly/1DYlh1Y ) reports that the Traverse City-based helicopter was a on a routine patrol when the crew spotted the wrecks and got pictures of them. The U.S Park Service, which manages the Sleeping Bear Dunes National Lakeshore, announced last month that the wreckage of the Jennie & Annie was now visible again on the beach halfway between North and South Bar lakes. Factors that include beach erosion, wind, waves and variable lake levels mean that various wreck fragments periodically become visible along the dunes shoreline.