Coming a year after an oil spill and six years after a hugely damaging hurricane, the Gulf oyster industry fears too much fresh water coming down the Mississippi River could be its final strike.

The Gulf lost half its oyster harvest last year, and is far from recovery now.

“The Louisiana and Mississippi oyster industries will be devastated by the opening of the Bonnet Carre’    Spillway,” says Gulf oyster expert Ed Cake.  “Too bad the Commission of Louisiana Department of Wildlife and Fisheries (LDW&F) refused to grant oyster fisherman east of the Mississippi River permission to transplant oysters from the state seed grounds in Lake Borgne before the freshwater kills them.  What a waste of the state’s natural resources, as well as the funds that were used to plant cultch on those seed grounds!”

To understand Cake’s concerns, one must first understand the flood control system that is being used to manage the water in lower Louisiana, which is getting its biggest test since the flooding that occurred in 1927, before any of these structures were existed.  Here’s a brief rundown on how it works:

Where the southwest corner of the state of Mississippi makes a tight fit with Louisiana, there’s a structure called the Old River Control Complex.  It’s the first of three monuments engineered to control one of the world’s most powerful rivers, the Mississippi.

Purpose of the Old River Control Complex is to divert 30 percent of the Mississippi River’s water to the west and down Atchafalaya River.  All water sent that way — and 620,000 cubic feet per second can be so diverted — will come out in Atchafalaya Bay almost 200 miles west of the Mississippi Delta.

Two other major structures that can divert the rising river are the Morganza and Bonnet Carre’ spillways.  The Bonnet Carre’ exists to save New Orleans by diverting 1.25 million cubic feet per second into the usually brackish and shallow Lake Pontchartrain. Its gates were opened on Monday.

The Morganza is located further upriver north of Baton Rouge and it’s opening, to send another 1.5 million cubic feet per second to the west and into the Atchafalaya, is expected shortly from the Mississippi River Commission in Vicksburg.

Oysters among all Gulf seafood are making the slowest recovery largely because river water was used after the April 2010 explosion on the Deepwater Horizon in an attempt to push back the BP oil spill to protect marshlands.  The action killed at least 80 percent of the oyster crop in the Barataria Bay and areas east of the river.

Coastal areas to the west, including Atchafalaya Bay, escaped direct impacts from the BP oil spill, which lasted for three months and put 4.9 billion barrels into the Gulf of Mexico.

Massive amounts of freshwater flowing down the Atchafalaya, which occurred only once before in 1973, could now devastate those oyster harvest grounds. Oysters cannot maintain their saltwater balances when hit with too much river water.

The damage from the flood control actions will set the oyster industry back by at least another year, experts say.  State biologists say the amount of damage will depend upon how long the diversions last and how much water is sent to places where it would not ordinarily go.

When the spillways were opened in 1973 — when flooding was less than this year — the action sent fresh water beyond the barrier islands in the Gulf.  Fresh water sunfish were being caught from those islands.

Young blue crab also need high salinity in their water to survive.  Shrimp and fin fish could be negatively impacted as well.

Ongoing research into the effect of the oil spill on marine life could also be compromised. 

Cake says after the “double whammy of Hurricane Katrina and BP’s oil spill and its aftermath,” Louisiana’s “precious oyster resources” are now again in harm’s way.