The association between abundance of invertebrates and presence of extensive periphyton cover in the Waitakere River (36° 28′S, 174° 31′E), northern New Zealand, was studied from October 1974 to June 1975. A black polythene canopy (44 m2) was placed across the stream, and the quantity of algal material and numbers of invertebrates in shaded and unshaded areas was measured. The presence of the canopy and the associated absence of periphyton influenced the distribution of several invertebrate species; those more abundant beneath the canopy wereSlavina appendiculata(Oligochaeta: Naididae),Austrosimulium australense(Diptera: Simuliidae), andAoteapsyche colonica(Trichoptera: Hydropsychidae), whereas the chironomidsMaoridiamesa harrisi(Diamesinae),Austrocladiussp. (Orthocladiinae), andParatanytarsus agameta(Chironominae) and the trichopteransHydrobiosis parumbripennis(Rhyacophilidae),Oxyethira albiceps(Hydroptilidae), andPycnocentrodesspp. (Conoesucidae) were more abundant outside.Potamopyrgus antipodarum(Mollusca: Hydrobiidae) andHydora nitida(Coleoptera: Elmidae), commonly recorded from algal mats in New Zealand, were equally abundant in shaded and unshaded areas. Differences in distribution between experimental and control sites may have been due to interference by periphyton with attachment sites (simuliids and hydropsychids) and feeding habits of the invertebrates (remaining species).