Biological studies in the main channels of the lower Mississippi and Atchafalaya Rivers below Cairo. Illinois. were summarized and reviewed with regard to their scope, methodology. and salient findings. The study area has received much less attention than the reach above Cairo, but 67 references were found to contain at least some direct mention of lower Mississippi/Atchafalaya River biota. Fishes are the best-known and most extensively studied organisms. although few intensive, standardized studies were found. The plankton community has received the most intensive study, largely through the National Water Quality Network program. Benthic invertebrates, commercial crustaceans, and aufwuchs are the least-known organisms, although certain recent studies have revealed general community/substrate associations.