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Montana Fish, Wildlife & Parks today said all fishing on the upper and middle reaches of the Big Hole River, totaling 47 river miles, will close effective Thursday, Aug. 10 at 12:01 a.m. due to extremely low flows and high water temperatures that threaten the river’s native Arctic grayling population. The fishing closure will extend from the Rock Creek Road upstream from Wisdom to Dickie Bridge on Highway 43 west of Wise River.

Fishing will continue on the popular sport fishery on the 102-miles of the lower Big Hole River from Dickie Bridge down stream to Twin Bridges.

"The Big Hole River Watershed Committee identifies when low river flows should trigger angling closures. These trigger points were met this week, placing the river’s grayling at risk,"   said Chris Hunter, FWP fisheries division administrator. Low water flows and high temperatures stress trout, making them especially vulnerable to disease and predators.

The Big Hole Drought Management Plan separates the Big Hole River into three "drought emergency" reaches. Today’s closure includes the 19-mile upper reach of the Big Hole River from Rock Creek Bridge, about five miles upstream from Wisdom, to the mouth of the North Fork; and the 28-mile middle stretch of the river that runs from the North Fork to Dickie Bridge on Highway 43, west of Wise River.

The upper reach of the Big Hole River recently reached temperatures above 70 degrees for most of the day.   On Sunday the upper river’s flow was measured at 18 cubic feet per second at Wisdom, below the 20 cfs closure trigger.

On the Big Hole’s middle reach, water temperatures peaked at 78 degrees, and also met the angling closure trigger of 60 cfs on Monday with fluctuations to a low of 30 cfs at Mudd Creek.  

The Big Hole River is critical habitat for Arctic grayling. The upper-most reach of the river includes most of the river’s grayling spawning and rearing habitat.

Hunter said the closure of the upper and middle reaches of the Big Hole are likely to remain in effect for the remainder of the summer. To reopen, the upper reach of the river must exceed 40 cfs for at least seven consecutive days with water temperatures that do not exceed 70 degrees for more than eight hours a day for three consecutive days. The middle reach would reopen when the river exceeds 80 cfs for at least seven consecutive days with the same water temperature guidelines.

Hunter said that it is likely that the middle reach of the Big Hole will recover more quickly and may be reopened first.

The Big Hole Drought Management Plan was developed by the Big Hole Watershed Committee, a group of volunteers representing agriculture, municipalities, business, conservationists, anglers and federal, state and local agencies.

Once abundant in the Missouri River above Great Falls, Montana’s native fluvial, or river-dwelling, Arctic grayling are now restricted to the upper Big Hole River. The population represents the last remaining native population of river-dwelling Arctic grayling in the lower 48 states.

The popular sport fishery on the lower reach of the Big Hole River from Dickie Bridge to the mouth of the river is open to angling. The flow on this reach of the river is at about 200 cfs at Melrose. The Big Hole River Drought Plan calls for closure of this reach at 150 cfs.

"Anglers should be aware of the low-flow conditions on the lower reach of the river and are urged to limit their fishing there to the morning hours when water temperatures are generally cool," Hunter said.