The first of Milwaukee’s many free outdoor bacchanals, RiverSplash! commences the summer festival season with three days of music, fireworks, junk food and large plastic cups of beer—all the good stuff. In addition to the requisite local cover bands, the festival organizers roped in an odd little headliner for tonight’s opening night: Buckethead, a masked, heavy-metal guitarist who endeared himself to the jam community with his elastic, virtuosic playing. He starts his set at 8:45 tonight.