Easing pressure on levees, raising environmental worries

NORCO, La. — When an 86-year-old flood control structure is opened northwest of New Orleans, it will lower the flood threat for that city, while raising environmental concerns.

The U.S. Army Corps of Engineers will open part of the Bonnet Carre (BAHN’-eh CARE’-ee) Spillway on Thursday. That will divert some of the rising Mississippi River’s waters north into Lake Pontchartrain and, eventually, into the Gulf of Mexico.

It will keep the powerful current of the rising river from putting a strain on New Orleans levees. But it also affects the salinity in the huge lake and in the Mississippi Sound, which can mean trouble for oyster harvests off the Louisiana and Mississppi Gulf Coasts. The river also carries nutrients that can cause algae blooms in the lake, which can lead to fish kills.