Saginaw Bay is a bay within Lake Huron located on the eastern side of the U.S. state of Michigan. It forms the space between Michigan's Thumb region and the rest of the Lower Peninsula of Michigan. Saginaw Bay is 1,143 square miles (2,960 km2) in area. It is located in parts of five Michigan counties: Arenac, Bay, Huron, Iosco, and Tuscola.
The Saginaw Bay watershed is the largest drainage basin in Michigan, draining approximately 15% of the total land area. The watershed contains the largest contiguous freshwater coastal wetland system in the United States. The Saginaw Bay Watershed Initiative Network  leads the effort to promote sustainable development in the Saginaw Bay Watershed by coordinating watershed programs and providing grants to innovative projects across the region.
 Origin of the name
O-Sag-e-non or Sag-in-a-we from the Ojibwa language, which means "to flow out", is a possible origin for the name "Saginaw". It may refer to the Saginaw River, which flows out into Saginaw Bay, and eventually into Lake Huron. The name "Saginaw" is not related to Saguenay, a region in Quebec whose name is of Algonquin origin.
The modern history of Saginaw Bay dates back to early 17th century. French explorers were the first Europeans to visit the Great Lakes region. The first European to visit the Saginaw Bay area was Father Jacques Marquette, a French missionary priest, who went there in 1668 after establishing a mission in St. Ignace. In 1686, father Jean Enjalran(fr) arrived in the valley to establish an Indian mission, but his efforts failed.
The region was ceded to Great Britain under the terms of the Treaty of Paris of 1763. Twenty years later, it was ceded to the newly independent United States of America. It became part of the Michigan Territory in 1805 and later the State of Michigan.
About 1813, Louis Campau erected an Indian trading post along the Saginaw River which led to the settlement of Saginaw in 1816, and to which the history of other settlements of Saginaw Bay area are rooted.
Saginaw Bay Light No. 1, a navigational light near the mouth of the Saginaw River, houses NOAA weather equipment providing weather conditions for the Bay. Gravelly Shoal Light, located near Charity Island, also houses a weather station.
- A World War II escort carrier was named Saginaw Bay.
- The Saginaw Bay Yacht Club remains one of the most prestigious in the region.
- Great Lakes Basin Program Projects, Great Lakes Basin Program for Soil Erosion and Sediment Control
- Saginaw River and Bay Area of Concern U.S. Environmental Protection Agency
- Sagninaw Facts and History Public Libraries of Saginaw
- Corelating the Orientation of Carolina bays to a Cosmic Impact: Saginaw Impact Structure
- Beacons in the Night, Michigan Lighthouse Chronology, Clarke Historical Library, Central Michigan University.