SILVERTHORNE — After a long drought, local anglers may once again soon be hooking feisty rainbow trout in the Blue River.

Hoping to rebuild wild populations of the popular game fish, the Colorado Division of Wildlife this week planted about 20,000 trout at three different spots along the Lower Blue north of Silverthorne.

“We’re hoping to see some decent survival,” said aquatic biologist Jon Ewert, after watching thousands of the five-inch trout splash from a hatchery truck into the chilly water below Dillon Dam.

The Blue River was once a stronghold for rainbow trout. Anglers who remember the good old days tell stories of three-pounders jumping acrobatically out of the water at the end of a taut line and flaunting their speckle sides against a brilliant Colorado sky.

But whirling disease, a crippling ailment carried by a parasitic worm, wiped out rainbow trout across the state after the spores accidentally were introduced to the state in a shipment of fish from an Idaho hatchery in the late 1980s. Ten years later, the fishery was decimated.

Since then, Colorado Division of Wildlife biologists have been working to breed a strain of rainbows that’s resistant to the disease and maintains some of the desirable fighting fish qualities of the Colorado River rainbows.

The Hofer strain, named for a German breed of trout that evolved with genetic resistance, show promise. Lab tests and experimental releases in the Colorado River show that the fish can survive and even reproduce in the presence of the disease.

“I think it’s great because, overall, we’d rather have wild fish and let them remain wild,” said Chris Hall, shop manager and guide at Cutthroat Anglers in Silverthorne. “It’s a necessary step to get rainbow populations back where they need to be. It’s going to take stocked fish to have wild fish again.”

Wild fish that have lived in the river their whole life are healthier and stronger, he said.

“With the Hofers, if everything goes well, we'll have natural reproduction and quality wild fish. This river needs a little help,” Hall said.

Gold-medal fishing

As it runs through Silverthorne, the Blue River offers gold-medal fishing, a rare designation meaning there is a dense population of big fish.

In recent years, those numbers slipped a bit, threatening the river’s gold-medal status. The loss of rainbows, fishing and poaching pressure on the brown trout population, along with drought and low flows, are probably the main reasons for the decline.

The fish planted this week are about five months old. In the state’s Rifle Falls hatchery, where they were raised, they grew about one inch per month. But in the cold Blue River, Ewert said he would be happy if they grew just a couple of inches in the next year.

It won’t be easy for the tiny fish. Big, brown trout lurk nearby, and the hatchery raised fish aren’t tuned into the hungry predators.

Ewert said he’d he happy to get a 10 percent survival rate, and that might be overly optimistic. The mortality rate for rainbow hatchlings in the wild is about 98 percent, he said.

Ewert will return to the Blue River in about a year and check on the survival and growth rate of the planted trout. It will take a couple of years before they are sexually mature, and the true test will be whether the rainbows reproduce.

In the meantime, anglers will keep their fingers crossed.

MORE INFO: Rainbow trout, whirling disease not native to Colorado

Rainbow trout all stem originally from the West Coast, primarily from a few rivers in northern California and Oregon. In the late 1800s, when fish husbandry became widespread, rainbows were transported all over the world. In Colorado, the rainbows became spunky, desirable game fish, and they are also long-lived.

Rainbows were also exported to Europe, where whirling disease was introduced into the mix. The spores that infect the fish are part of a complex lifecycle involving mud-loving tubiflex worms. Over time, some of the European rainbows evolved with a resistance to the disease.

Working with scientists through an international collaborative, Colorado researchers started to do some genetic testing to try and find the exact genes that make the German trout resistant. The first crosses between the Colorado River rainbows and the Hofer rainbows were made in 2003, with 35 different "families."

Using genetic markers, the scientists will be able track the offspring from those pairings, even after the fish have been released into the wild. Currently, there are two field trials in progress, in the Gunnison and South Platte rivers.

Part of the challenge was that the resistant Hofer strain was long bred as a docile food fish. The differences are even apparent in a lab setting, where the Colorado River rainbows tend to try and hide in the farthest corner of a tank. But the Hofer rainbows are nearly tame.

The Colorado research has important implications for fisheries across the country. Whirling disease is still spreading," said Dave Kumlien, director of the Montana-based Whirling Disease Foundation. "This is the only tool resource managers have for managing rainbow trout fisheries in the wild," he said.