The Hawaii Department of Land and Natural Resources said Thursday that thousands of black-chin tilapia have invaded near-shore waters in the Napali Coast State Wilderness Park on Kauai.

According to a press release, fishermen first reported seeing large schools of “mostly juvenile tilapia” over the past two weeks.

“While these might originally be viewed as an introduced species to Hawaii they are definitely in this case an invasive species,” said Ka‘ili Shayler, a Fish & Habitat Monitoring Coordinator with DAR.

Tilapia are mostly freshwater species, and the invading fish may have come from a ditch system on the west side of the island. It’s speculated that the tilapia may be moving to areas where freshwater meets the ocean.

DLNR said it plans to take “aggressive steps to try and stop” the invasive fish from moving further either direction.

DLNR Chair Suzanne Case said, “The Napali Coast State Wilderness Park is among the most pristine, in-tact, natural areas in all of Hawaii. It’s absolutely critical that we aggressively address any new invasive species threats and with this invasion of black-chin tilapia, that is precisely what we’re planning.”