Early 18th-century maps show Borgne as a true lake, largely separated from the gulf by a considerable extent of wetlands that have since disappeared.

The primary causes of wetland loss in the basin are the effects of natural changes to the topography over time and can and will change in the future, the hydrological isolation of the Mississippi River from its floodplains (which deprives the coast of sediment needed to build and sustain land), and the extensive cutting and channelization of coastal wetlands (which destabilizes existing land, hastening the transition to open water).

The construction of the MRGO, which breaches the natural barrier of the Bayou La Loutre ridge and the Borgne land bridge, has allowed sea water to push farther into the basin.

[3] Since 1932, approximately 24% of the Borgne Land Bridge has been lost to severe shoreline retreat and rapid tidal fluctuations, and the loss rate is increasing.

These land bridges prevent estuarine processes, such as increased salinity and tidal scour, from pushing further into the middle and upper basins.