This should generate some discussion! A friend of mine and I were fishing pool 4 between the “Y” and the locks the other night just to check it out. My jig snagged on the bottom and when I pulled it back up it was covered in black grease. At first I thought it was just black weeks but when I pulled them off my hands looked like I had been working on an old car. And it was black grease.
I can imagine where it came from. Is the whole bottom of the channel covered with that stuff?