Down on the Bayou

From May, 1997 (Update #30)

An effort to ward off damage from spring floods may inadvertently introduce zebra mussels into previously uninfested Louisiana waters. In March, for the first time since 1983, the Mississippi River's high waters prompted the opening of the Bonnet Carre Spillway, which is located 25 miles northwest of New Orleans. The spillway routes water from the Mississippi to Lake Pontchartrain, thereby protecting New Orleans from flooding. With the spillway diverting 15% of the entire river's flow in late March, "[The Bonnet Carre] became a major arm of the Mississippi," said Bruce Thompson of the Louisiana State University Coastal Fisheries Institute. The U.S. Army Corps of Engineers closed the spillway (which was open for one month) on April 17, at which time officials indicated they had no plans to re-open it again this year. Since the lake serves commercial and recreational users, boating activities could spread zebra mussels further upstream into tributary rivers. "Opening the spillway is responsible for the distribution of fauna and flora," noted Thompson. "The potential impact could be considerable." Very little Mississippi River water normally enters Lake Pontchartrain, therefore the lake has been protected, thus far, from zebra mussel infestation. Due to water exchange with the Gulf of Mexico, salinity varies throughout the lake and it is unclear whether zebra mussels will be able to thrive. Another confounding factor is the presence of other mollusks that produce veligers, which will make zebra mussel veliger identification difficult. Yvonne Allen of the Louisiana State University Fisheries Research Institute works with Thompson to monitor for zebra mussels. Allen reported that veliger counts in the Mississippi River during the spillway diversion were very low, around one per liter. However, she cautioned that "logs, bottles and other debris with attached zebra mussels" could also bring the mussel to Lake Pontchartrain. With financial support from the Lake Ponchartrain Basin Foundation, Thompson and Allen will be monitoring several stations in the lake this summer in an attempt to determine whether opening the spillway helped colonize the lake with zebra mussels.

ID: 199705-4.

The Zebra Mussel Update was a 4- to 8-page quarterly national newsletter published by the University of Wisconsin Sea Grant Institute from May 1990 through May 1997. The ZMU documented the spread of the zebra mussel -- an exotic nuisance mussel -- through North America's freshwater environments, especially the Great Lakes, and on efforts to control it.