Eusthenia nothofagi is a species of stonefly in the family Eustheniidae. It is endemic to Australia, where its range is restricted to Victoria. It is known only from the Otway Ranges and its common name is the Otway stonefly. This insect lives in streams in temperate rainforest dominated by myrtle beech (Lophozonia cunninghamii) and wet sclerophyll dominated by mountain ash (Eucalyptus regnans). This species was described to science in 1979. It is similar to , but its wings are more red than solid purple.