“Another possible factor impacting walleyes is increasing water clarity – Northern waters becoming clearer because of better land management (including better septic tanks). Walleyes have sensitivity to light and if that light is penetrating deeper in the water it could upsetting their life cycle.”
They are experiencing that here on the Yakima River in Eastern Washington. The Yakima is a slow moving river and most always dingy brown from sediment runoff from irrigation return water. Modern farming practices have removed the heavy sediment load and now the river is clear. A few years ago the Dept. of Ecology proposed to eliminate phosphorous in the in waste water returns to the river because the river is now full of algae and other aquatic plant life because with the new clarity and sun light is causing them to bloom.
Well, is there a lot more cover and brush in the bodies where the walleye are doing well compared to the others?
While I don’t know about inland lakes and streams but the zebra mussels could also be a factor. The zebra mussels feed at the bottom of the food chain taking food from normal prey of the Walleye.
I think about it every time some genius tells us how great the mussels are because they can see the bottom of lake Erie 30 feet down.
I doubt better septic tanks are the culprit for cleaner water. There are many very very large lakes with few septic tanks in the area. Certainly not enough to have much of an impact. At least for many lakes in the north.