Rocky riffles in rivers support a complex community of algae, bacteria, fungi and detritus often held together by a polysaccharide matrix. This biofilm provides food for invertebrates, some fish, platypus, rakali and turtles. Biofilms are scoured naturally by high flows. River regulation alters the timing, duration and frequency of biofilm scouring. Environmental flows downstream of dams, including translucent and transparent releases are designed to restore some of the variability of flow and allow scouring to reset early-stage biofilm, which is more palatable for aquatic animals.

IMEF biofilm and invertebrate studies were performed in the Hunter and Murrumbidgee Rivers, testing the hypothesis (IMEF Hypothesis 4) that restoring some freshes and high flows would induce scouring of silt and biofilms and improved habitat quality for some invertebrate scrapers and their predators.

Sites located on the Murrumbidgee River downstream of Burrinjuck Dam, received periodic environmental releases, between April and October, as well as irrigation flows and uncontrolled spills. Riffle rock biofilms, aquatic invertebrate metrics and water quality were compared with reference sites on the unregulated Goobarragandra and Goodradigbee rivers. Control sites were chosen on the Tumut River, which is regulated by Blowering Dam but unlike the Murrumbidgee River did not receive variable environmental releases.

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