LIVINGSTON, Mont. — Tens of thousands of dead fish have closed Montana’s Yellowstone River and stirred new worries Monday about lasting impacts to the region’s lucrative outdoors industry.

Gov. Steve Bullock declared an “invasive species emergency” over an aquatic parasite blamed for the dying fish. A 183-mile stretch of the Yellowstone and all waterways that drain into it have been closed since Aug. 19 to prevent the deadly parasite from spreading. The unprecedented move came after thousands of dead mountain whitefish started washing up on the river’s banks downstream from Yellowstone National Park.

Smaller numbers of other fish species have been killed. That’s offered hope that the parasite will spare the trout populations that made the Yellowstone a destination for fly fishers from around the world.

But uncertainty over how long the closure will remain in force — and whether the parasite will crop up again in future years — has unsettled those whose livelihoods depend on the river.

Fishing guide Chase Chapman of Livingston said he’s losing tens of thousands of dollars’ worth of business as customers cancel previously booked trips. The losses are likely to grow as the closure continues, he said. Yet Chapman is not interested in training for another occupation and foremost wants to know when the river will re-open.

“I don’t think anyone wants re-training,” Chapman said Monday, during a workshop in Livingston for affected workers that was hosted by the state Department of Labor and Industry. “We all have established businesses. We’re not going anywhere…. Now what do we do?”

Monday’s emergency proclamation from Bullock will allow Montana to spend up to $15.4 million on worker retention grants and other programs meant to blunt the economic harm of the closure, state officials said.

The number of people and businesses that lost work over the closure has not been tallied, said Scott Eychner, workforce services administrator of the state labor agency. Eychner said officials did not want to wait until that information was tallied before holding Monday’s workshop, so that assistance could be given to those who need it as quickly as possible.

Repairing the river’s reputation is another matter.

Paul Weamer, who manages a fly fishing shop in the Paradise Valley north of Livingston, said he has no doubt the Yellowstone and its fishery will recover. But Weamer said news reports of the fish kill have left a negative impression among outsiders that will be hard to overcome even when the Yellowstone reopens and fishing resumes.

“You hear dead fish and that freaks people out and I understand that. But I really think our fishery will be good next year,” Weamer said.

State officials on Monday said infected fish have been discovered in Laurel, more than a hundred miles downstream from the epicenter of the fish kill. A small number of whitefish that were collected near Laurel have tested positive for exposure to the parasite, officials said.

Whitefish exposed to the parasite also were collected near Columbus, Big Timber and at the mouth of the Boulder River, but officials said all the downstream fish were still alive and appeared healthy.

The rate of fish dying appears to have eased in recent days, said Sam Sheppard, regional supervisor for Montana Fish, Wildlife and Parks.

Sheppard added that it was too soon to say if the decrease in deaths would prove lasting.

Officials have warned outbreaks of the parasite are possible in future years now that it’s been established in the Yellowstone.