Fighting a swamp thing in Texas

CADDO LAKE, Texas - At first glance, it looks like a beautiful addition to the water: a floating fern with small, bright green leaves.

But when Robert Speight saw just a few sprigs of the plant on Caddo Lake for the first time late last year, his heart sank.

“When I saw it here,” Speight says, “I knew we were in for a long, tough battle.”

The little fern, known as giant salvinia, is like something out of a science fiction movie. Biologists call it the world’s worst weed. The plant has the uncanny ability to reproduce itself rapidly. One plant can become 60 million in less than two months. A handful today will cover more than 40 acres in just a few weeks time.

Left unchecked, the invasive plant forms giant mats on top of a water surface, smothering all life below.

“This is the most sinister aquatic plant I’ve ever dealt with,” says Randy Westbrooks, an invasive species specialist with the U.S. Geological Survey. “It takes no prisoners.”

Giant salvinia is native to the Amazon region of Brazil, where it’s kept in check by natural forces, namely a Brazilian weevil. The invasive plant was first discovered in the U.S. in a pond in South Carolina in 1995. Biologists believe it may have hitched a ride in a shipment of Brazilian lilies. Without a natural enemy, the small fern began spreading exponentially. The plant has been reported in a handful of lakes and streams from the Carolinas to California. Anywhere it ‘s spotted it brings trouble, as some say, like a green creature from the deep.

“You have to take it seriously, just like a disease, and get rid of it as fast as you can,” Westbrooks warns.

Robert Speight maneuvers his small boat through the chocolate-brown water of Caddo Lake, past the cypress trees covered in Spanish moss, until his boat is surrounded by a carpet of green. He turns off the boat motor before it becomes clogged by the giant salvinia floating on the water.  “This is the mature plant,” he says as he leans over, sticking his hand through the green layer to scoop up a handful.  “It’s starting to fold on itself and get to the clumping or matting stage,” he says.

Speight looks out beyond his boat to the lifeless water around him.  “It will actually block out the sunlight, block out the oxygen in the water. The fish and animals die,” he says.  “I’ve been on Caddo Lake all my life; I got my first boat when I was seven.  This stuff scares the hell out of me.”


Caddo Lake is the largest naturally-formed  lake in Texas and, arguably, one of the most beautiful. It straddles the Texas-Louisiana state line. Giant salvinia has been found on the Louisiana side of the lake, where the water is generally more open. Speight, who is chairman of the Greater Caddo Lake Association, lives on the Texas side, where shallow bayous and sloughs would be the perfect breeding ground for the foreign fern.  He and others would like to rid the lake completely of giant salvinia, but short of that, they want to keep it out of the Texas side.

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