Montana is closing a 175-mile stretch of the Yellowstone River to all recreational activities to prevent the spread of a parasite that is believed to have killed tens of thousands of fish, authorities said Friday.

The action is needed to prevent the spread of the parasite that causes proliferative kidney disease and to protect the fishery and the outdoor economy it sustains, said Fish, Wildlife and Parks officials. The closure extends from Yellowstone National Park's northern boundary to Laurel, along with tributaries in those areas.

Over the past week, wildlife officials have documented more than 2,000 dead mountain whitefish and believe the total number killed is tens of thousands of fish. The agency has begun receiving reports that the die-off is beginning to affect some rainbow and Yellowstone cutthroat trout.

The closure means fishing, wading, floating and boating are not allowed on the river.

"We recognize that this decision will have a significant impact on many people," FWP Director Jeff Hagener said in a statement. "However, we must act to protect this public resource for present and future generations."

Fishing guide Dan Gigone of Livingston says the closure will be catastrophic for his industry.

Gov. Steve Bullock said a threat to Montana's fish populations is a threat to the state's outdoor economy and the jobs it sustains.

The wildlife agency will monitor the river and will lift the closure when stream conditions, such as flow and temperature, improve and fish mortality ceases.

It has set up two decontamination stations near the affected area to try to reduce the chance of equipment spreading the parasite to other rivers. The agency is asking the public to properly clean all equipment prior to moving between bodies of water.