Creature from the Green Lagoon

Caddo Lake in Texas is suffering under an alien invasion. Giant salvinia was imported from South America as an ornamental plant for aquariums and lawn ponds, but some escaped in 1998 and invaded a Houston pond. In 2006 it started moving from lake to lake and has become the scourge of Texas wetlands.

Australian researchers have calculated that, given the right conditions, an M&M-size salvinia plant could blanket 39 square miles of water in just over three months. As the advancing front reaches maturity, it swells into a carpet of vegetation up to three feet thick, smothering other life in its path by consuming nutrients and blocking sunlight from penetrating the water below. Fish can’t survive. Native plants and amphibians struggle. Lake recreation halts as viny roots clog boat engines and become ensnared in propeller blades. In some areas, the dense layer of salvinia can even become a substrate for other opportunistic weeds, making it difficult to tell where the lake ends and the shore begins.

People who live among the lakes have tried many ways to control salvinia: sweeping it up in nets, building barriers, and even blowtorching it. Importing weevils seems to be the best bet, but even that program has drawbacks: lack of government funding, a climate that salvinia survives better than weevils, and the fact that importing one invasive species to get rid of another can have devastating consequences. Read about the invasion of giant salvinia at Texas Monthly.