To put it simply they both changed things. The clean water act cleaned up the water and made it an better environment on Lake Erie. Lake Erie is very fertile and with the fertility the walleye population exploded. But the visibility was never that much and a lot of walleyes where caught but drifting and casting. The best year class to date was 1988. The zebra mussels came in and changed the environment again. By filtering the water they reduced the fertility and made the water clearer. This changed the fishing but didn't clean the water. Now walleye are still caught drifting and casting but a lot of trolling is done with boards to get lines away from the boat. This is needed with the clearer water. In Lake Michigan the zebras mussels have filtered the water so much that there are days I can see 40' down, but that is a different story.
