Typically the bite on the lake this time of year can be tough as most of the walleye head upstream to spawn and will make their way back into the lake in mid-May. If you are trying to target walleye on the lake look near the dam, beaches, and anywhere there are rocks for the walleye to spawn on or near. For a lot of action fishing below the dam is excellent in April and May, the drum will make you go crazy as you may catch 50 of them a day but there are some good walleye, crappie, pike, and whitebass to be caught this time of year. Jig and minnow is the best method usually fished vertically or pitched on the seam of the fast water. 3-way rigs and trolling lead core up and down the river work great especially in front of the bubble and in front of the Nebraska fishing pier.
If you are eager to chase this walleye up river. The Santee Bluffs and where the Niobrara River dump are the typical spawning locations and there can be some nice walleye caught this time of year. The low water levels are making it very difficult to navigate so go at your own risk but I don't recommend running your fiberglass boat up there unless you know where you are going. A flat bottom boat is the ticket.