Eunotia cataractarum belongs to the E. exigua complex based on size, striae density and valve constricted before the apices. The ventral margin of E. cataractarum is not as strongly concave as that of other members of E. exigua species complex. Furthermore, the apices of E. cataractarum are more rounded and not as strongly dorsally recurved compared with E. exigua. Finally, the shoulder is steeper in E. cataractarum valves compared with the more gradual slope in the E. exigua valves. While E. cataractarum is similar to E. varioundulata, the dorsal margin of E. caracatarum is flatter and lacks undulations. The dorsal margin of E. cataractarum is not straight as that of E. orthohedra.