An analogue of the Hawking effect, whereby black-body radiation is emitted by black holes, can be seen in general wave phenomena when analogue horizons are present as waves propagating on a stationary counter-flowing medium. When the flow matches the speed of the wave, the wave is blocked and converted into other branches of the dispersion relation. L-P Euvé of CNRS-Université de Poitiers in France and colleagues have now observed this phenomenon in the power spectrum and two-point correlation function in surface waves on a countercurrent of water in a linear tank. Furthermore, because the flow velocity near the blocking point decreases along the direction of flow, the system is in fact an analogue of a white hole (a time-reversed black hole).