When it was built just before the Civil War, the Nottoway Plantation House had about 80 acres of front yard between it and the Mississippi River. Today a dike that protects Nottoway from the Mighty Miss fills most of that area.

Nottoway has not changed much since slaves built it in 1857. It survived the Civil War with only a couple of raids by Union calvary and some potshots by passing gunboats. Tour guides this weekend, however, are worried about that dike being breached by record-high waters coming down the Mississippi River over the next few days.

By May 22, the Mississippi will crest at 17 feet over flood stage at New Orleans. The levees that were last breached by Hurricane Katrina are designed to hold back a 20-foot river.

When the Army Corps of Engineers, which manages this river, starts opening and closing structures like the Bonnet Carre Spillway, things start to happen. Nottoway might stay dry, but fresh water will start replacing salt water in all the mushy areas that mark where the river ends and the Gulf of Mexico begins.

For those looking to harvest oysters and shrimp, that is not good news. The season lost by the BP oil spill could become the season lost by Mississippi flooding.

Opening up spillways sends nitrogen-rich river water into Lake Pontchartrain, pushing out the brown shrimp that enjoy the brackish waters. Fisheries experts do not see the impacts as being long-term, but they can disrupt one’s season.

That’s something the local seafood industry does not need. Louisiana figures its harvest was down last year by 37 percent for shrimp and 39 percent for crab; and 23 percent for finfish. Its oyster harvest was off by 49 percent from both the oil and flushing fresh water into the Gulf in an effort to keep the spill off the coast.

The rebound that’s underway does not have anyone doing handstands. When you visit fishing areas, like Yscloskey in St. Bernard Parish, the people you meet working the boats look mostly worried.

Nor can the Gulf seafood industry feel good about 41 percent of restaurateurs responding to a Louisiana Restaurant Association survey by saying “seafood safety perception” is the top challenge they face. The optimists among them point out the lack of evidence about an actual seafood safety problem.

Hearing that the Mississippi is rising by one foot a day is enough to make one who has no stake in these waters feel a little anxious. No wonder all those oystermen and shrimpers might feel a little overwrought. As much as they need to rebuild their sales, they especially need a year or two without a disaster in it.