As the Kenai Peninsula’s lakes ice over, the three in which the invasive waterweed elodea were found this summer have been largely freed from infestation, according to Kenai National Wildlife Refuge Supervisory Biologist John Morton, who belongs to the group of ecological managers leading local efforts to exterminate the weed.

In February 2017, Alaska Department of Fish and Game workers discovered elodea growing beneath the ice of Sport Lake, which is heavily visited in the summer by boaters and fisherman drawn by its state-maintained boat launch and Fish and Game-stocked population of coho and rainbow trout. Elodea grows in thick columns that can suffocate fish and entangle boats and floatplanes. Able to reproduce by fragmentation, elodea has spread through Alaskan lakes via boat propellers and floatplane rudders, and has been the target of a statewide eradication campaign since 2012.

Unlike native flora, elodea survives and continues to photosynthesize through the winter beneath ice. Kenai National Wildlife Refuge staff found it in six of the 28 ice-holes they drilled around Sport Lake’s perimeter in March. The spring thaw revealed floating mats of the weed.

Staff from the Refuge, the Alaska Department of Natural Resources, and the Kenai Watershed Forum released the elodea-killing herbicides diquat and fluridone into the lake in May. The most recent application was on July 16.

“When we redid our surveys here by the end of September, we only found elodea in two spots,” Morton said. “And the elodea we pulled up was only a single strand of brittle elodea… Things are looking really good for Sport Lake — I think we’ve succeeded there.”

Early in the summer, the Alaska Department of Fish and Game stationed an employee at their popular Sport Lake boat launch to spoke with boaters and check for elodea fragments caught in propellors or boat trailers. By July 10, Morton said, the herbicides had killed enough elodea that the launch could reopen without an attendant.

Kenai Watershed Forum Invasive Species Specialist Jen Peura talked with Sport Lake property-owners about the treatment efforts and looked for clues about the elodea’s origins by interviewing some of them.

Floatplanes are a potential spreader of elodea, and Peura said Sport Lake had five docked there last summer. Most of their pilots were willing to talk with her, though some weren’t, she said.

“No one wants to be blamed, and that wasn’t what I was going after,” Peura said. “But if it was brought in from somewhere, where could it potentially have been brought from, and if it did end up leaving there, and we ended up infecting another lake from the Sport Lake population, where potentially could that be? And the hardest thing to track would be with floatplanes — they’re the longest range vector we have.”

She wasn’t successful in getting information about the infestation’s origin.

“Sport Lake is such a popular lake, and has such a high amount of traffic, that it could have come from anywhere, really,” Peura said.

While elodea was being treated in Sport Lake, Peura was also carrying out plans to survey a list of 25 other high-risk lakes. On July 27 she found elodea in two of them — unnamed on official Kenai Peninsula Borough maps, but known locally as Hilda and Seppu Lakes.

A system of marshes connect these lakes with Beck Lake — one of the three Nikiski lakes where the first elodea infestations on the Kenai Peninsula were discovered in 2013 (the other two were Stormy and Daniels Lakes — by 2015 elodea was eliminated from all three with the same herbicide treatment used in Sport Lake). Morton said Hilda and Seppu Lake were surveyed for elodea in 2013, and though none was found, he suspects based on its present abundance that they were infected at the time.

Within a week, the Cook Inlet Aquaculture Association — a partner in previous anti-elodea efforts — put up two nets in the surrounding wetlands to prevent elodea fragments from spreading. Under an emergency permit exemption from state herbicide regulators at the Alaska Department of Environomental Conservation, Refuge staff treated the two lakes with fluridone and diquat.

On Nov. 1 — just before the water iced over for probably the final time this year — they made a second fluridone deposit in the lakes, which will continue killing the elodea under the ice through the winter. Morton said there will likely be another fluridone treatment when Hilda and Seppu Lakes thaw in the spring.

The Kenai Peninsula was an early leader in elodea eradication, thanks in part to a $40,000 grant from the Kenai Peninsula Borough Assembly in 2014, Morton said. Keeping local lakes clean is a losing battle, however, if the highly-transmissible weed becomes prevalent in other parts of Alaska. Though the herbicide treatment has proven effective, a need for funding has kept it from being applied in other areas of the state — such as Fairbank’s Chena Slough and parts of the Mat-Su Valley — that are also infected with elodea.

“We’ve done well to date,” Morton said. “If another infestation shows up, we’ll jump on it as well. But we can’t keep this up forever. The ultimate strategy is to get the rest of the state to catch up.”

Reach Ben Boettger at ben.boettger@peninsulaclarion.com