By Dylan J. Darling • The Bulletin

Hoping to rid another Central Oregon lake of a prolifically reproducing nonnative catfish, Oregon Department of Fish and Wildlife officials are considering pouring rotenone into North Twin Lake next fall.

Derived from South American rain forest trees, the toxic chemical suffocates anything with gills. Brown bullhead catfish are overrunning North Twin Lake, so Fish and Wildlife plans to kill all fish in the lake and then restock it with rainbow trout, a popular sport fish, said Brett Hodgson, district fisheries biologist for the agency in Bend.

“Really the only effective way to be able to start with a clean slate and meet fishery management objectives is to remove (the catfish) completely,” Hodgson said.

The decision on whether to treat North Twin Lake should be made by next February or March, he said. Over the past six years, Fish and Wildlife has treated three other Central Oregon lakes with rotenone to wipe out the same kind of catfish — South Twin Lake in 2011, as well as Antelope Flat Reservoir and Walton Lake in 2009. North and South Twin lakes are about 40 miles southwest of Bend, close to Wickiup Reservoir.

The agency also used rotenone to kill 90 million tui chub, an illegally introduced bait fish, in Diamond Lake in 2006 and a small population of goldfish in a pond near Crane Prairie Reservoir in 2011.

“When you do the treatment, you basically do an ecological reset for the entire water body,” Hodgson said. He did not have estimates for how many catfish were in South Twin Lake or are in North Twin Lake.

So far the treatments have been successful, Jessica Sall, ODFW spokeswoman in Salem, wrote in an email.

“The response from the rainbow fishery (at the lakes) was rapid and dramatic.”

Two years after the treatment at South Twin Lake, anglers reported hauling in 24-inch, 3-pound rainbows, Hodgson said.

Since the rotenone treatment and restocking at South Twin Lake, fish caught there have been nice and healthy, said Joanne Frazee, who owns Twin Lakes Resort with her husband, Jim Frazee. The resort is on the west shore of South Twin Lake.

“I know that the public seems to be pretty happy fishing there last year and the year before,” she said.

Sall wrote that the other lakes were producing rainbow trout more than 20 inches in length within a year after the treatment.

“There appears to be a trend where the most dramatic improvement is in the first 3-4 years after treatment and then things tend to normalize (still much improved from pre treatment conditions),” she wrote.

The catfish in North Twin Lake probably were illegally introduced by someone hoping to foster an illicit fishery. Hodgson said some people like to fish for and eat the fish, which come from the Southeast and Midwest. The fish first appeared in Central Oregon at Prineville Reservoir in the 1970s and have since been found at other lakes. Wickiup Reservoir also has the catfish, but Hodgson said there are no plans to treat it with rotenone because it feeds the Deschutes River and supplies irrigation water.

While the catfish are big for a couple of years after being added to a lake, their average size shrinks as the number of fish in the waters grows.

“If they have been in a water (body) for a while you will rarely see one over 8 or 10 inches,” Hodgson said.

Treating a lake with rotenone is not only drastic, but it also can be expensive. The rotenone alone for South Twin Lake cost about $130,000, Hodgson said. It then also took two days of work by a Fish and Wildlife crew.

He estimates treating North Twin Lake would cost about $200,000 for the rotenone alone. It would also require three days of work for 12 to 20 people.

“It’s a pretty big lake, it’s deep and it would be a fairly expense project,” Hodgson said. The treatment is usually done at the end of the season, late in the year, and the lake is ready to restock the next year.

There are other options when it comes to dealing with an unwanted fish problem such as the brown bullhead catfish. They include trapping or netting the fish.

Fish and Wildlife opted to trap tui chubs in East Lake, west of La Pine, after determining rotenone treatment there likely wouldn’t kill all the fish because of the dynamics of the lake, Hodgson said. Springs feed the lake, giving fish a refuge from the toxic chemical. Trapping at East Lake started in 2010 and is ongoing.

The ODFW probably will opt to treat North Twin Lake, as it did South Twin Lake, with rotenone because it will be less labor-intensive and more effective than manual efforts, he said.

“Once they get established it is extremely difficult if not impossible to get rid of them without the chemical treatment,” Hodgson said.

— Reporter: 541-617-7812,

ddarling@bendbulletin.com

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