Aquatic insect larvae play an important role in travertine deposition at Louie Creek, a small, karst spring-fed stream in northwest Queensland, Australia. The most conspicuous larvae are the caddis-flies, of which the genus Cheumatopsyche is the most abundant. These larvae build retreats consisting of travertine and organic fragments harvested from the stream bed. Silken nets constructed across the retreat opening act as food traps and as important substrata for calcium carbonate precipitation. The nets and retreats together form distinctive microtopographic features that not only disturb hydro-dynamics, and thus probably stream chemistry, but also contribute significantly to travertine deposition rates under a range of hydro-chemical conditions.