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:''This article is about the bay in Michigan; see Thunder Bay for other things with a similar name.''
'Thunder Bay' is a bay in the U.S. state of Michigan on Lake Huron. The bay extends from North Point at to South Point at .
The city of Alpena lies at the mouth of the Thunder Bay River at . The entire bay lies within Alpena County, with Alpena Township in the north and Sanborn Township in the south.
Several islands in the bay are protected as part of the Michigan Islands National Wildlife Refuge. Thunder Bay Island lies just east of North Point outside the bay. The wildlife in the Bay's waters are protected as part of the Thunder Bay National Marine Sanctuary.
The name is the English translation of the French ''Anse du Tonnerre'', which appears as early as the map of Franquelin in 1688. It was probably derived from the Native American name, as they believed that the Bay was peculiarly subject to thunder storms.