The Mississippi River diversions are intended to build new land by diverting floodwaters from the river into open water, wetlands there. Since oyster cultivation depends on the oyster beds seeing a narrow salinity range, there is a concern that the diversion of river floodwaters into the base will destroy the oyster industry.
Understanding the problems of oyster cultivation in Louisiana starts with remembering that large oyster beds are not native to the Mississippi Delta:
There are vast areas of soft mud bottoms, in your State, which may be made just as productive in oysters as is the ground of Messrs. McLaughlin & Lobrano and others, but not until vast quantities of sand and shells are deposited upon them, and they are effectively protected by locks and dams from fresh water floods, and this fresh water is regulated and utilized either in fattening the oyster or in protecting the beds from an excess of salt water after a severe “norther.” (First Annual Report 1902-1904 Oyster Commission of Louisiana)
The proponents of river diversions argue that they mimic the natural processes of the Delta. This is not a good thing for oysters. Sediment in the river floodwaters can smother the oyster beds. The dramatic changes of salinity that accompany large floods of freshwater can also damage the oyster beds.