Region. Months. Species...whatever you want to make it!
Best and Worst Times of the Year to Fish!
My experience says that the worst time to fish is right after ice-out. The best, here in C. Wis. and in N Wis. is June, but July, Aug., Sept are also good. Also in C. Wis. early ice is almost always better than late ice. That's been my experience. Also, I'm targeting panfish, and am lucky once in a while to catch bass or northern when fishing for panfish, and I release those anyway. Waxies and minnows in the winter, crawler pieces and minnows in the summer, occasionally leeches. That's my story and I'm sticking with it.
Most enjoyable days are Sundays after Labor Day. Half of the idiots have closed their cabins up for the year and won’t be seen again until Memorial Day. The other half of the idiots are indoors watching a Packer game. The only ones who are on the water are serious about what they are doing and you rarely have to deal with getting cut off or being crowded.
Best: anytime there is open water. Worst: anytime there isn't open water.
Best time to fish: any time I can't go. Fish will be completely suicidal.
Worst time to fish: any time I can go. Fish will all have lockjaw.
I've fished most of the last 50+ years in northern WI. I was raised on the shores of a chain of lakes and had the opportunity in my youth to fish every day the weather, school and my mood would permit, and some days I tempted fate with the weather. In that time I've picked up a piece of knowledge or two and one of those tidbits is that no matter the time of year, you can always get on to some good fishing.
On more than one occasion I've had fast fishing casting in open water while the lake across the road, sometimes even connected, still had walkable ice. I've broken ice at a landing in the fall to get out to some great fishing. I have been on shaky ice both early and late when I've done well.
I think the problem some folks run in to is when they pigeonhole themselves and try to catch fish in places the fish aren't or by using tactics the person is used to but the fish aren't interested in at that time of year or in that place.
There really is no "Bad Time".
You have to fish different places.
If the lakes get tough or in transition?
Hit a river.
Edit:We're blessed with the Great Lakes also.
Worst time of the year: right before ice up and right after ice out. Best time of the year: if you can't catch a fish in June in Wisconsin you probably shouldn't fish! Everything seems to bite in the month of June!
Species: Anything that bites.
Best Times: December, Late ice. Mid May-June. September.
Worst Times: 3 weeks after ice out (Now!) . 1 month before ice up until about three weeks after the ice has been on.