Caddis-fly larvae (Order: Trichoptera; Family: Hydropsychidae; Genus: Cheumatopsyche) build distinctive nets and retreats on the surface of tufa deposits in spring-fed rivers of the Barkly karst, northern Australia. Their activities are confined specifically to swiftly flowing reaches, where the nets and retreats form linear arrays arranged almost perpendicular to stream flow. The arrays become encrusted by calcium carbonate and, when high-velocity conditions are maintained, are succeeded by the next generation of caddis flies. The arrays are well preserved in many fossil tufa deposits, where their alignment and long-section morphology indicate paleoflow direction at the time of caddis activity. This can assist in the paleoenvironmental reconstruction of fossil tufa sequences.