More than 6,000 virus-infected African clawed frogs were euthanized over the summer in a Washington State pond, The Olympian reported.

The frogs are predatory, invasive and reproduce quickly. A stormwater pond system near Saint Martin’s University in Lacey had 6,106 of them. The frogs tested positive for ranavirus, which causes systemic infections in a wide variety of saltwater fish, The Olympian reported.

The City of Lacey worked with the state Department of Fish and Wildlife to come up with a plan to trap, test, contain and eliminate thousands of the amphibians from three ponds at the College Regional Stormwater Facility, City Manager Scott Spence said Tuesday.

The frogs were euthanized by increasing the salinity of a large, upper pond, said Doug Christenson, water resources engineer for Lacey. Next summer, city and wildlife officials will focus on the smaller east and west ponds.

The frogs were first discovered in late summer 2015 by a member of the state Department of Ecology, who recognized the frogs as not being native to the area, Christenson said. It was thought to be the first time an African clawed frog has been found in the state, he said.