I would contact Lakeside bait at Waukegan harbor, and ask for an update.
You are a little early but if you go out of Waukegan ,troll south towards Great Lakes toward the white tanks. Try 20-30 ft of water first, on top with yellowbirds and shallow running dipseys. I would troll flies( tinsel-silver/green or silver blue, and orange 00 dodgers, very slow troll doing an s-pattern troll ! If no luck try going al the way to the front of Great lakes harbor and stay shallow. If no good try moving out deeper 10-20 ft at a time. Remember to keep those flies 18-24 inches behind the dodger ! Shorten your leads in May when the water warms up . If the water is to dirty in shallow, then try and find the cleaner water in the least amount of depth ! Vary your yellow bird distances till you can establish a pattern.