HOUSTON (AP) — Texas wildlife officials said Monday that an invasive shellfish marching through the state’s waterways “present an immediate danger” to other wildlife, and extended emergency rules designed to prevent the zebra mussels from wreaking havoc on the state’s water-based economy and ecosystem.

The shellfish are believed to have first invaded the Great Lakes by traveling in ballast water of cargo ships arriving from Europe through the St. Lawrence Seaway in the mid-1980s. Since then, they have reached all five lakes, invaded major rivers, including the Mississippi and the Hudson, and have recently reached the West Coast, likely by attaching themselves to the hulls of cruise ships.

Experts say the zebra mussels have caused hundreds of millions of dollars in damage by clogging power plants and pushing out native species. The U.S. Fish and Wildlife Service estimates the mussels have caused billions of dollars of damage nationwide.

David Jude, a fisheries biologist at the University of Michigan who has researched and dealt with the impacts of the mussels on the Great Lakes ecosystem, was unavailable for an interview by The Associated Press. However, he emailed one comment to the AP: “Beware the zebra. Impending doom.”

The Texas Parks and Wildlife Department fears that the mussels, which were found in two Texas lakes in mid-July, will spread south. The emergency rules — which took effect without the usual 30-day notice due to the urgency of the situation — require boat owners take special measures to empty out water-holding receptacles aboard their vessels and bars people in certain vulnerable areas from removing live nongame fish from the water.

The agency is asking for water to be removed from boats before moving from one area to another because the mussels’ larval stage is free-floating and microscopic and can be unknowingly transported. The department is responsible for overseeing state parks, issuing fishing and hunting licenses and caring for a variety of wildlife.

The zebra mussels, according to the Department of Natural Resources, feed by drawing in water and filtering out microscopic plants, animals and debris. This depletes plankton in the water and can decrease food available for other aquatic life, including fish. It also makes the water clear, allowing light to penetrate and help more plants to grow, possibly interfering with larger predatory fish, as well as anglers, swimmers and boaters.

The mussels are the only freshwater mollusks that can attach to solid objects, one of the reasons they spread rapidly — and far.

“Once zebra mussels become established in a water body, they are impossible to eradicate with the technology available today,” the Texas parks agency said in its emergency rulemaking.

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