If the river is the Saginaw, then it's full of old trees from the logging days and Dioxin and other chemicals from the Dow Chemical plant upstream. Suction dredges are not crazy about the trees it seems.
The levels of Dioxin (think Agent Orange) recently found in roughly six pockets along the river are many times the allowable federal limits, this despite several clean up efforts in the past. The river has also been cleared of logs many times in the past, but somehow they keep popping up.
From Saginaw downriver to Bay City and Saginaw Bay the river bed is also full of heavy oil and metallic deposits from numerous manufacturing facilities that sprung up in the area. I've watched numerous freighters deliver loads of stone, gravel, various ores and salt to terminals in and below Saginaw. The ships propellers really stir up the bottom, particularly when they come in full.
There are several other smaller rivers that feed into the Saginaw, these drain basically the entire center of Michigan and these streams are heavily polluted as well. Most are now much better than they were years ago with the closing of many chemical plants and refineries and with the addition of anti-pollution and dumping laws since about 1970.
Two rivers in this system I can think of also have natural underground salt seeps that contribute salt and other minerals into the water. Let's just say you do not want to swim in or drink the water……
Lots of history along and in Michigan's rivers.
