Sprol

In this zoomed out view you can see the city of Detroit and part of the freshwater Great Lakes system. The color difference in the urbanized area has more to do with poor false-color matching than any blight or devastation, despite how it looks. The devastation here is in the water.

The smaller body of water on top is Lake St. Clair, the biggest smallest lake in the Great Lakes system. In other words, it’s the biggest great lake that’s not a Great Lake. As such it probably doesn’t get enough respect. It should– in the upper right you can see the largest delta system in the Great Lakes, and by extension and in fact, the largest freshwater delta system in the world.

And it’s dying. It certainly doesn’t look healthy. We’ll return to this in a moment.

One side of the above image is the United States. The other side is Canada. Can you guess which is which? People with a primary school education shouldn’t be guessing. Yep, that’s the USA to the north, with Canada just over the river to the south offering low sales tax and good deals on pharmaceuticals, among other things.

Okay, same question. This one is a little more difficult. In this case, that’s canada on the right, and the United States territory to the left of the river. It’s a trick question of course, because that area west of the river is actually an indian reservation.

So all of that cultivated land produces runoff that includes quite a lot of the chemical fertilizer, made from natural gas with anhydrous ammonia as an intermediate step. It washes out of the soil and into that great freshwater delta system.

Normally a delta and the surrounding wetlands purify and detoxify the nitrates in the water and act as a living filter, like the Florida Everglades. With all of that artifical fertilizer draining into the river and through the delta, the concentrations exceed the tolerance of the plant and animal life in the wetlands. As a result, they die, which you can see here.

In addition, the extra nutrients in the lake create an anerobic "dead zone" in the deep parts of the lake, which are shown here in black. Microbes in the water multiply to consume the nutrients, using up all of the oxygen in the cold, deep waters of the lake. Anything that gets caught in this water winds up dead. This is the "Dead Zone" problem that has been popping up more and more lately.

The Michigan portion of the delta has been urbanized, while Ontario has set aside much of the wetlands as the Walpole Indian Reservation. Wetland loss from urban and recreational encroachment continues to be a problem on the U.S. side; and in Ontario, many of the wetland areas have been wiped out by agricultural drainage. source

Not that the agriculture is the only problem, of course:

Agriculture is the predominant land use within the river’s watershed. But, intensive development has occurred in and near the cities of Port Huron and Sarnia. The heaviest concentration of industry (including a large petrochemical complex) lies along the Ontario shore near Sarnia. Several communities along the St. Clair rely on the river as their primary source of drinking water. Industries — including petroleum refineries, chemical manufacturers, paper mills, salt producers and electric power plants — need high quality water for their operations as well. Ships carrying cargo between the upper and lower Great Lakes ply the St. Clair River.
St. Clair River RAP priorities include contaminated sediment remediation on the Canadian side of the river, elimination of CSOs and SSOs on both sides of the river, elimination of spills to the river from "Chemical Valley" downstream of Sarnia, Ontario, and ensuring proper notification when spills do occur. US Environmental Protection Agency