OAKWOOD, Md. (WHTM) — Maryland officials are warning of a possible northern expansion of an aggressively invasive species into the Susquehanna River.

The Maryland Department of Natural Resources said a partnership overseeing fish passage at the Conowingo Dam reported that 81 northern snakeheads were caught in the dam’s fish lift this spring, a dramatic increase from the one snakehead found there during the past two years.

All known snakeheads were stopped and killed before reaching the dam’s reservoir, officials said. The hydroelectric dam on the Susquehanna River is about five miles from the Pennsylvania line.

The fish lifts were installed on the east and west sides of the dam decades ago to allow passage of migratory fish such as American shad and river herring. The lifts operate during the spring migration, which is also when snakeheads are known to travel longer distances.

One snakehead was observed in the lifts in 2017.

Northern snakeheads, sometimes called “Frankenfish”, were first observed in Maryland waters in 2002. They have been found in several parts of Pennsylvania since 2004, including the Octorara Creek in Lancaster County, which empties below the Conowingo Dam.

The species native to China is a voracious predator of fish, freshwater crustaceans, and amphibians. Wildlife experts say if introduced, its populations could become established throughout most of the United States.

Because of their feeding style, biologists say snakeheads could out-compete popular sport fish such as largemouth bass. Experts are also concerned that the fish could introduce parasites and diseases that could harm native species.