00:35 Scores of Fish Dying in Montana River Tens of thousands of fish are dying in Montana’s Yellowstone River, forcing officials to close a nearly 200-mile stretch to water activities.

At a Glance Tens of thousands of fish are believed to have been killed recently by a parasite in the Yellowstone River.

The river, known for its world-class trout fishing, will remain closed until officials can confirm the parasite is gone. Nearly 200 miles of the Yellowstone River have been closed, in addition to hundreds of miles of other waterways, as biologists attempt to stop the spread of a parasite that's believed to have already killed tens of thousands of fish.

The closures will remain – possibly for months – until the fish deaths end, according to officials from Montana Fish, Wildlife and Parks. The ban includes all river activities, including fishing and rafting.

A big concern among officials is that the fish kill could have a lengthy impact on the river's reputation as one of the best trout fisheries in the world, which draws visitors from all over.

“This kill is unprecedented in its magnitude ,” Montana Fish, Wildlife and Parks spokeswoman Andrea Jones told the Bozeman Daily Chronicle. “We haven’t seen something like this in Montana.”

(MORE: Typhoon Makes Direct Hit on Tokyo, Closes Airport )

<img class="styles__noscript__2rw2y" src="https://dsx.weather.com//util/image/w/fishing_3.jpg?v=at&w=485&h=273&api=7db9fe61-7414-47b5-9871-e17d87b8b6a0" srcset="https://dsx.weather.com//util/image/w/fishing_3.jpg?v=at&w=485&h=273&api=7db9fe61-7414-47b5-9871-e17d87b8b6a0 400w, https://dsx.weather.com//util/image/w/fishing_3.jpg?v=ap&w=980&h=551&api=7db9fe61-7414-47b5-9871-e17d87b8b6a0 800w" > In this Sept. 9, 2004 file photo, three fishermen float down the Yellowstone River. (Garrett Cheen/The Livingston Enterprise via AP) (Garrett Cheen/The Livingston Enterprise via AP)

The closures extend to hundreds of miles of waterways that feed into the Yellowstone, including the Boulder, Shields and Stillwater rivers.

No dead fish were found inside Yellowstone National Park, where a celebration of the National Park Service’s 100th anniversary is set for next week and no closures were planned there.

The parasite causes fish to contract a fatal kidney disease and die. FWP spokeswoman Andrea Jones said the disease can have a mortality rate as high as 90 percent. Other places that have had similar outbreaks include Washington State, Oregon, Idaho, Canada and Europe.

Reports of the Yellowstone river fish kill began pouring in more than a week ago. Wildlife officials confirmed more than 4,000 fish deaths, but they say the toll is probably much higher.

Most have been mountain whitefish, a native game species, but reports emerged that the die-off has affected some rainbow trout and Yellowstone cutthroat trout species crucial to the fishing industry.

MORE ON WEATHER.COM: Yellowstone's Volcanoes