In a natural river many shallows, sandbanks and islands occur, which is unfavorable for shipping at low water levels. Groynes have the task of keeping the river at depth. Groynes on both sides of the river narrow the gully, the water flows faster and the river deepens. Thanks to the groynes, trade across the Waal can largely continue even in dry times. But because the river channel is kept exactly in place, at depth and at the correct flow rate, much of the natural variation along the river has disappeared. In recent decades there has been a growing call to allow more natural dynamics along the river and thus to have watercourses of different depth and with variation in flow speed. This provides room for more plant and animal species in the floodplains.