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Details About The Invasive Plant Floating In Bayou St. John

Travis Lux
A mat of giant salvinia floats underneath the Magnolia Bridge on Bayou St. John on February 4th, 2019. The invasive species is found around Lake Pontchartrain, and recently took up residence on the waterway.

For the past couple weeks, a mass of green plants has been floating down Bayou St. John in New Orleans. Residents have been wondering what it is, and whether it poses any threats to the waterway.


To get some answers, WWNO’s Travis Lux went down to the bayou with Dr. John Lopez, coastal program director for the Lake Pontchartrain Basin Foundation.

The following transcript has been edited for length and clarity:

Q: This is the stuff that’s been floating around the bayou. What is it?

It’s a floating aquatic plant, which means it doesn’t root in the ground. The plant itself -- the species -- is what’s called giant salvinia. It’s an invasive plant. It’s not something that’s found in Louisiana. It was introduced, we believe, about 20 years ago. We’re now finding it in Bayou St. John.

Q: You said it’s not native to Louisiana, but are we finding it in other bayous around the state?

Yeah, basically any of the swamp or marsh areas around Lake Pontchartrain or areas around New Orleans that are fresh, you’re subject to finding it now. It’s very similar to water hyacinth. A lot of people are familiar with water hyacinth -- that’s also an invasive plant. It was introduced over 100 years ago.

Q: When you use the word “invasive” -- that sounds like an inherently negative thing. I know some people in the area have been concerned that maybe it’s bad for the bayou. Maybe it’s bad for plants or fish, or maybe it could hinder recreation. Are those things that people should be concerned about?

You’re correct, the term “invasive” does have a negative connotation and actually, it’s meant to be that way. You can have introduced species that are not considered invasive because they don’t necessarily cause problems, but it’s not bad in an extreme sense.

It [salvinia] can cause problems -- especially if it forms very dense mats. It can cause the water below to become stagnant, maybe low in oxygen. So it can reduce the water quality.


Also, it’s more of a navigation issue if it’s very dense. Boaters could have trouble going through it -- canoers, kayakers. And you certainly don’t want to be swimming in that because it would physically be very hard to swim through. You don’t want to do that.

Q: What about water quality? What does this tell us about the water quality -- whether it’s poor or healthy?

I don’t think it says too much in this case. Plants need nitrogen -- it’s a fertilizer for growth. Sometimes the growth can be caused by fertilizer in the water. In this case, we don’t think the nitrogen levels are abnormally high. There is nitrogen in the water, but we believe it’s a normal level. Actually, the plants are helping remove that nitrogen, so in some ways there’s a little bit of benefit there.

Q: What can be done about it? Do you have to just leave it there, or can it be removed?

Invasives are, in most cases, impossible to eliminate. We wish it could be otherwise, but that’s just kind of the reality. Once they get into the natural system, it’s very hard to eradicate them -- to eliminate them entirely. So you have to manage it.

Louisiana Department of Wildlife and Fisheries is going to be treating this. I think they’re looking at a number of options to help contain it. They’re looking at a program to try and manage it.

Also, there’s kind of a mechanical aspect. In this case you have a floodgate [at the mouth of Bayou St. John on Lake Pontchartrain]. The levee board [Southeast Louisiana Flood Protection Authority - East] has agreed to work with us. They have to operate the gate to make sure it’s working properly for our flood protection. We all know that’s extremely important. They’re going to work with us when they want to schedule an opening to make sure there’s not any problem with hyacinth or salvinia, to try and avoid incidental introduction.

But it’s going to be there. This is not the first time salvinia has been in Bayou St. John -- it’s been here before. There’s different ways that it can be transported, aside from being pushed in by the floodgate. So it’s something that we’ll just have to manage going forward. Everyone that we’re talking to -- the levee board, Wildlife and Fisheries, City Park officials, the neighborhood, kayakers -- everyone seems to want to join in and help with that process.

We’re pleased that people have that interest and are willing to talk about it, tell us about it, and work with us to try and solve the problem.

Support for the Coastal Desk comes from the Walton Family Foundation, the Greater New Orleans Foundation, the Foundation for Louisiana, and local listeners.

As Coastal Reporter, Travis Lux covers flood protection, coastal restoration, infrastructure, the energy and seafood industries, and the environment. In this role he's reported on everything from pipeline protests in the Atchafalaya swamp, to how shrimpers cope with low prices. He had a big hand in producing the series, New Orleans: Ready Or Not?, which examined how prepared New Orleans is for a future with more extreme weather. In 2017, Travis co-produced two episodes of TriPod: New Orleans at 300 examining New Orleans' historic efforts at flood protection. One episode, NOLA vs Nature: The Other Biggest Flood in New Orleans History, was recognized with awards from the Public Radio News Directors and the New Orleans Press Club. His stories often find a wider audience on national programs, too, like NPR's Morning Edition, WBUR's Here and Now, and WHYY's The Pulse.

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