Tidal deltas are characterized by a dendritic network of distributaries that transport water and sediments to the ocean. Here, I show that the distributaries self-organize to uniformly redistribute the tidal prism across the entire delta system. The 2 opposite mechanisms of channel formation by avulsion and channel abandonment drive the entire delta toward a critical state at which every channel is close to the silting threshold. Under these conditions the delta reaches self-organized criticality, with changes of its planimetric channel distribution occurring across several spatial scales.