Earlier this year, Brandy Branch Reservoir, a 1,242-acre power plant lake near Marshall, was temporarily closed because of the discovery of an invasive exotic plant called giant salvinia.

Non-native plants and wildlife are expanding across America, usually with a negative impact. As spring weather encourages boating and fishing, boaters should remain alert for invasive species and report sightings to the proper authorities. Here is a question-and-answer session on the subject with Earl Chilton, Texas Parks and Wildlife Aquatic Habitat Enhancement Program director.

What are the top exotic species of concern in Texas?

The exotics TP&W has found most problematic include hydrilla, water hyacinth, giant salvinia and giant reed (a major problem on the Rio Grande). Of course, we are concerned about zebra mussels, Pacific oysters, invasive tenicates, armored catfish, snakeheads, etc.

How effectively have we controlled giant salvinia since it was first identified at Toledo Bend Reservoir, and how many lakes have had a confirmed salvinia sighting?

Giant salvinia is controlled much more easily on Toledo Bend when we are helped out by fluctuating water conditions. Those years with a near-constant water level are generally the years when giant salvinia expands. In addition to Toledo Bend, giant salvinia has been confirmed at Brandy Branch Reservoir, Caddo Lake, Center City Lake, Lake Conroe, Lake Palestine, Pinkston Lake, Sam Rayburn Reservoir, Shelton Reservoir, B.A. Steinhagen Reservoir and Lake Texana.

How much money are we spending to control exotics in Texas?

Spending really depends on the year and the availability of funds. TP&W spends thousands each year on habitat surveys, but much of the cost of herbicides and other controls, including grass carp, is borne by our cooperators, per state recommendations. However, TP&W alone spends several hundred thousand dollars each year, including salaries, treatments and surveys.

How do the plants affect fishing and boating activities?

Giant salvinia, hydrilla and water hyacinth can severely inhibit boat traffic, skiing, swimming, fishing, jet skiing, etc. Excessive growth of hydrilla can be hard on boat motors and water hyacinth can grow so thick that it's difficult to get an airboat through it. Additionally, these plants can affect water quality. In some cases, fish kills may occur due to lack of oxygen as a result of overabundant plants.

What's the worst-case scenario for giant salvinia?

In some places around the world, giant salvinia has been known to completely cover large areas. For example, at one point, giant salvinia covered an estimated 96 square miles of the Sepik River in New Guinea. Similarly, it infested about 200,000 acres of Lake Kariba on the Zambezi River. When giant salvinia grows that thick, there is no mechanism for oxygen exchange into the water, and fish either die or try to move out from under the weed if possible.

What should boaters and anglers do to make sure they do not spread these noxious plants?

Be aware of potential dangers and laws concerning transporting aquatic plants (intentionally or accidentally). Learn to identify the most dangerous plants. Avoid boat ramps infested with invasive plant species. Check and clean the boat, motor, trolling motor, live well and trailer before leaving an area known to harbor invasive plant species. Encourage others to do the same.

Aside from humans, how does hydrilla and giant salvinia spread?

It is possible for mammals, birds and other organisms to transport exotic species. One property owner told us he saw a cow bring giant salvinia to his pond from a nearby swamp. The plant was stuck to the cow's leg. Within weeks, the entire six-acre pond was covered with giant salvinia.

Where can you find the best illustrations of exotics?

One of the best Web sites is http://plants.ifas.ufl.edu/photocom.html for the University of Florida.