River 'Tsunami'

I was astonished, this week, as I pumped water from the Klein River to my one-ton tank. As if I were witnessing the approach of a tsunami, the entire river drained before my eyes (see the photo of my hose pipe in the drained river). This must be about one kilometre from the river’s source. OBSERVATION: This river is vital to the most diverse riverine ecosystem in the world, and someone has the power to turn it on and off over its first kilometre? (Not to speak of my needing water).