Surf Langenfeld isn't a river wave at all — it's a standing wave built into a cable water-ski lake between Düsseldorf and Köln that's been running skiers and wakeboarders for decades. The adjustable surf wave sits alongside six tow cables, and it's forgiving enough that beginners can be up and riding within a session or two. There's an entrance fee, but between the Seehaus restaurant, the beach bar, and the lakeside paths, it makes for an easy day even if the wave isn't firing exactly how you want. Open year-round, it's a solid backup when the rivers are blown out or running low.