After being hit from both sides with invasive species, Stormy Lake may finally be on the mend.

Stormy Lake, one of the larger lakes in the Captain Cook State Recreation Area on the north side of the Kenai Peninsula, has been blocked off to public access since 2012. The Alaska Department of Fish and Game began treating the lake with the piscicide rotenone, a fish-killing chemical, to eliminate the invasive northern pike.

During the treatment, another invasive species was found: elodea, a troublesome aquatic plant that had infected multiple lakes across the peninsula.

In 2013, Fish and Game reintroduced arctic char, Dolly Varden, rainbow trout and longnose suckers back into the lake.

They’re now growing very well — some are up to 19 1/2 inches, said Robert Begich, area biologist for Fish and Game.

“The fish restoration of Stormy Lake has been very fast,” Begich said. “We put fish back into the lake, and plus the stream that flows from Stormy Lake into Swanson River, allowing fish in the river to recolonize the lake.”

Approximately 7,000 arctic char fingerlings were reintroduced to Stormy Lake in spring 2013. The fish grew rapidly in the first two years and have moderated since, according to Robert Massengill, a fisheries biologist for Fish and Game based in Soldotna.

The surge in growth may be partially due to a lack of competition for food, Massengill said. The native rainbow trout and juvenile coho salmon populations were low at the time of reintroduction, he said in an email. A rush of scuds — freshwater shrimp — in 2013 also likely served as a good food source for the young char, he said.

“Sometimes following a rotenone treatment to kill invasive fish, the fish carcasses remaining in the lake can provide a short-term fertilizer effect that spurs food production,” Massengill said. “It is possible that happened in Stormy Lake.”

Arctic char typically grow slowly in sparse populations, according to a Fish and Game fish directory. However, the Stormy Lake breed is genetically different than other specimens of the subarctic fish. They tend to be two to three times the size of other species of arctic char, ranging up 8 pounds, Begich said.

“Stormy Lake is a unique fish,” Begich said. “We don’t know the degree of how much genetic separation is among the char in all the lakes, but we know that there’s different forms in all the lakes.”

Begich said rotenone-treated lakes can offer fish a “pristine” start, which could have contributed to the fast recolonization as well. However, the lake is not ready to reopen to public access yet. The removal of the pike also offered an opportunity to juvenile coho salmon — with the predators gone, it’s likely that the population will increase, because the salmon use the lake and the Swanson River drainage as a spawning ground, Begich said.

Although the elodea infestation, which was treated with the herbicide fluridone throughout 2013 and 2014, is very likely gone, biologists want to be extra sure there are no plants left before they reopen the boat launch, said Kenai National Wildlife Refuge Supervisory Fish & Wildlife Biologist John Morton.

“For all practical purposes, we do think it’s gone,” Morton said. “But with this much money, we do really want to make sure it’s gone. But we really expect Stormy Lake to be open in the spring for the public.”

Morton said samples had shown no elodea in nearby Daniel’s Lake, but Stormy Lake received treatment later than the other lakes in the area, so they plan to do spot treatments before the winter sets in to maintain the fluridone levels in the lake. Keeping the fluridone levels at a predetermined level — approximately 10 parts per billion, he said — for a long time will ensure that the elodea dies without killing other native plants.

In some ways, it was lucky for the arctic char that Stormy Lake had an elodea invasion, Morton said. Because the lake has been closed, it allowed the fish to grow without the threat of being harvested, which may have contributed to how fast they have grown and repopulated.

“That’s a good story, because those char have grown big even as we’ve been treating it with fluridone,” Morton said. “It’s reassuring to the public because it shows that fluridone doesn’t actually impact the fish.”

Begich said char have grown the largest, but coho salmon, rainbow trout and Dolly Varden have also successfully recolonized the lake. However, Fish and Game still plans to issue an emergency order prohibiting retention for the winter, as they have done for the past three years. Ice fishing is permitted with two closely attended lines, provided only one hook or artificial lure is used on each line.

Meanwhile, biologists will be sampling the lake each week to determine the size of the char when they reach maturity, Begich said. Fall is spawning season for arctic char.

“We want to take it slow, and we want to prohibit the retention for the winter,” Begich said.

Reach Elizabeth Earl at elizabeth.earl@peninsulaclarion.com.