The long-term consequences of eutrophication in estuaries may include reduced biodiversity, increased dominance of opportunistic species, and changes in material and energy flows. It has become increasingly apparent that these symptoms of eutrophication are not minor and localized, but have large-scale implications and are spreading. The estuaries and coastal waters of the northern Gulf of Mexico (GOM) are classic examples of these phenomena. Concerns for the Barataria and Breton Sound Estuaries targeted for "restoration" by increased inputs of Mississippi river water thus include possible eutrophication and hypoxia, probably in localized areas.

Eutrophication can also stimulate HABs and HAB toxin production. Phytoplankton toxins have been the subject of regional interest for many decades in the Gulf of Mexico. Clearly, large rivers like the Mississippi can have a significant impact on biological processes in the coastal zone and shifts in nutrients within estuaries may promote growth of potentially toxic algal species. Besides HABs, pathogenic Vibrio bacteria can also pose health risks in coastal systems. Infection by Vibrio vulnificus is one of the leading causes of seafood-related illnesses in the United States.

Anabaena sp. (HAB)