SUMMARY. 1. During a 2-year study of the fish and macroinvertebrates of a third-order montane stream, a severe drought in the first year resulted in a temporary cessation of surface flow. Flow was continuous during the second year.
2. Some taxa (e.g. Ophiogomphus severus) exhibited higher density during the drought year, others declined in abundance during low flow (e.g. Baetis spp.), whereas a few (e.g. Tricorythodes minutus) appeared unaffected. Total macroinvertebrate density decreased by 50% during the low flow year compared to the normal flow year. Mayflies were most severely affected, but also exhibited the most dramatic recovery.
3. The collector-gatherer functional feeding group was abundant only during the normal flow year, whereas shredders and predators exhibited increased relative abundance during low flow.
4. Fish populations were severely reduced in the low flow year. However, fishes rapidly invaded the area following resumption of normal flow.