A watershed is an area of land that drains to a particular body of water, river, or lake. Everybody lives in a watershed. The history of the Saginaw Bay Watershed is relatively short and one of continued change. The Saginaw Bay was covered by glacial ice until about 11,000 years ago. As the glaciers retreated the size and the shape of the Great Lakes varied greatly. The Saginaw Bay was larger at first, it then went dry, and was eventually refilled about 6,000 years ago. The modern Great Lakes did not take their present shape and drainage patterns until about 3,000 years ago.
Prior to European settlement http://www.codesria.org/IMG/pdf/2-3.pdf the Saginaw Bay was home to a diverse aquatic and wildlife population. In the environment created from the retreating glaciers caribou, elk and mastodons thrived. It was the pursuit of these animals that brought the first humans to Michigan. As the post glacial fir and spruce forests disappeared in the Saginaw Bay Watershed they were replaced with various hardwoods, lake plains and wetlands. The Bay and its tributaries became filled with an abundance of fish species. Rock reefs in the Bay https://www.mlive.com/news/bay-city/index.ssf/2018/04/epa_grants_1_million_to_rebuil.html and the abundance of freshwater tri
butaries were excellent spawning grounds for a variety of fish. The inner portions of Saginaw Bay contained walleye, yellow perch, catfish, and suckers. The Outer Bay was home to great abundances of Lake Trout, Ciscoes (Lake Herring), and Whitefish. When European settlers arrived in the Saginaw Bay region they began to harvest these species just as the native peoples of the area had been doing for thousands of years. A commercial fishing industry flourished with the peak harvest year in 1902 of 14.2 million pounds of fish being taken from the Bay.
Along with a vibrant aquatic environment the Saginaw Bay watershed prior to European settlement was also home to a great variety of waterfowl, reptiles, other bird species and mammals. The numbers and health of many of those species have been impacted by the changes in their environment in the last 150 years.
The early European interest in the Great Lakes region centered on businesses and industries that took advantage of the vast natural resources found there. Travel was mainly conducted on the extensive tributary system of the Saginaw River. The Saginaw River is one of the deepest in Michigan. This enabled multiple industries to develop in the Saginaw Valley over the last two hundred years because of the access to national and international markets through shipping.
The first Europeans who came to the Saginaw Valley were trappers and traders of animal furs. Of these the first settlers were traders who established trading posts with the native Indians for these furs. Louis Campau established a trading post in Saginaw in 1813 and Jacob Smith established another in Flint in 1819. Following the construction of Fort Saginaw in 1822 the military constructed a crude road from Smith’s trading post in Flint to Saginaw that winter. John Jacob Astor’s American Fur Company made him the first multimillionaire in America thanks to his Michigan operations which established an early trading post in Midland in 1831. However the area was difficult for habitation due to the swamps and the mosquitoes found in them. Many early travelers and settlers suffered from malaria that was caused from these mosquitoes. Major Baker the commander of Fort Saginaw said of the area “nothing but Indians, muskrats and bull-frogs, could possibly subsist here.” Alexis de Tocqueville wrote of the mosquitoes in the Saginaw Valley, “Their presence would suffice to render a long sojourn there insupportable.” The subsequent drainage of many of the swamps brought the mosquitoes and the malaria they carried under control.
As the fur industry began to decline in the Saginaw Valley the lumber industry quickly replaced it. The first lumber mills were built in Flint in 1830 and Saginaw in 1835. The lumber industry dramatically transformed the Saginaw Watershed over the next 60 years. The peak year of lumber production was in 1882 with over a billion board feet of timber being milled in the sawmills along the Saginaw River. The drainage of the swamps and the lumbering of the land left the land accessible to settlement by farmers. Because of these factors the Saginaw River system began to experience significant silting problems.
The chemical manufacturing industry also began to see substantial growth in the Saginaw Valley. After the success of the first deep brine well in Midland in 1879, Michigan quickly became the world’s leader in salt brine related products. In 1888 Midland was the world’s leading producer of Bromine and in 1897 the Dow Chemical Company was formed. Another industry which began to flourish was the manufacture of transportation products; the first of these was the carriage and next was the automobile. Flint was the center of the automobile activity in the Saginaw Valley with the creation of Buick Motor Car Company in 1904 and eventually General Motors in 1908. Multiple automobile and parts manufacturing facilities were created in Flint, Saginaw, and Bay City in the twentieth century. 
The automobile and chemical manufacturing industries have led to the contamination of the Saginaw River and Bay Watershed through the discharges from their manufacturing processes. The agricultural industry, especially as it entered the last half of the twentieth century, began to impact the watershed through the runoff of commercial fertilizers and pesticides as well as silt. As early as the 1930s large fish kills were being reported along the Saginaw and Cass Rivers. Also the commercial fishing industry saw significant declines in fish populations in the 20th century. In the 1970s high levels of DDT and PCB in fish were making them unsafe for human consumption. The waterways of the Saginaw River system had connected the regions communities and industries with the world through the Saginaw Bay; this also meant that the contaminants from the whole watershed were transported and concentrated in the Saginaw River and Bay.
2013 ariel view of Saginaw Bay with visible silt and contamination plumes flowing from multiple rivers into the Saginaw Bay.