Government scientists and Trout Unlimited (TU) announced Tuesday that costly efforts to remove invasive lake trout from Yellowstone Lake to protect native fish populations are working. The number of invasive fish are declining and young cutthroat numbers are rebounding.

Lake trout, a fish known for its voracious appetite, appeared in Yellowstone National Park’s 132-square mile lake in 1994, and posed a threat to the region’s fragile populations of native cutthroat. Since then, crews have netted and removed about 1.4 million lake trout. But the endeavor costs approximately $2 million annually–an amount some critics say is too much to spend to expunge a fish prized by anglers elsewhere, The Associated Press reports. The Yellowstone region supported a recreational fishery valued at $30 million annually before 1994.

“I’m very encouraged by some of our recent successes,” said David Hallac, chief of the park’s science center. “The goal is to crash the population of lake trout to a point where they are no longer adversely impacting Yellowstone cutthroat trout.”

Officials expanded the netting program in recent years, but a TU scientist noted it’s unlikely lake trout can be eradicated from the lake and will require some type of management in the future to protect cutthroats. One method may include using electricity to destroy lake trout eggs–a reportedly less-expensive deterrent than netting.