What happened to Mark Twain and the Crappie Fishing?

Several years ago, my wife and I (we live in Illinois) fished for Crappie at Mark Twain several times a year, and it was never hard to limit out in no time. It didn't matter the time of year or the time of day, you could always catch a mess of fish. Then for 3 or 4 years after that, it's like the Crappie picked up and left? What happened?