Abstract: An echo chamber including a high-strength, structurally rigid receptacle and a weight bearing grate through which the water from an artificial outdoor waterfall may pass, which grate can support considerable weight loads exerted by materials such as rocks, stones, and the like. The receptacle functions as a substitute for a flexible artificial waterfall water sump liner and receives recirculating water of an artificial waterfall. When constructing a disappearing artificial waterfall using a chamber constructed according to the present invention, rocks or other material are placed on the chamber's grate. As water cascades through the material on the grate and falls into the chamber, an echo sound is generated. Differing configurations of the stones on the grate and changes in water level in the receptacle produce echoes of different pitch and intensity.