For the second time in less than three months, the Bighorn River's flow has fluctuated wildly because of a U.S. Bureau of Reclamation error, stranding and killing fish.

The Bighorn River is considered a multimillion-dollar resource because of its attraction as one of the Montana's top trout fisheries. The stream also provides irrigation water for agricultural lands downstream from Yellowtail Dam.

"There were lots of young-of-year rainbow and brown trout in little puddles," said Ken Frazer, fisheries manager for Montana Fish, Wildlife and Parks in Billings after visiting the river on Wednesday. "A couple of the big puddles had big fish stranded in them."

The problem occurred Tuesday while drawing down the Afterbay for a seepage test, according to Tom Sawatzke, deputy area manager for BuRec. When the problem was noted, operation was switched from the Consolidated Operations Center in Casper, Wyo., back to the local crew. Sawatzke said the error had nothing to do with gate automation, which caused the problem in July. Back then, the river flows quickly fell from 4,000 cubic feet per second to 1,500 cfs, stranding small fish in backwaters and along the bank.

Flows were inadvertently increased Tuesday from about 3,000 cfs to 4,435 cfs, Sawatzke said. When the error was noted, the flow was reduced to 1,385 cfs before leveling out at 2,000 cfs, he said.

"They really yo-yoed it," Frazer said.

"We ran into some difficulties getting the test conducted as scheduled," Sawatzke said.

A U.S. Geological Survey hydrograph for the river showed the flow plummeting even lower, to 800 cfs, then climbing before falling to 700 cfs. No explanation for the discrepancy in figures was immediately available.

The problems on Tuesday started about 12:45 p.m., Sawatzke said. The test was concluded at noon on Wednesday and flows were being stepped back up to 3,300 cfs, he said.

"It's not as easy as it sounds when you're trying to balance the level of the river, reservoir and power generation," Sawatzke said. "I wish it wouldn't have been as large as a flow fluctuation as it was, but it was only for a short period of time."

Frazer of FWP had worked with the Bureau of Reclamation for three weeks to ensure the test went smoothly. He said the flows were going to be stepped down incrementally to avoid stranding fish.

"This is pretty definite evidence that there's a lack of communication between the Montana and Wyoming offices running this thing," Frazer said. "The Wyoming people don't understand the operation of this system."

Frazer said he hopes the effect on the fishery won't be too dramatic, since there seems to be lots of fish in the system. He said the Bighorn is a very productive stream, as long as there is plenty of water.

"We'll just keep pointing out that we need better communication," he said.

Contact Brett French at french@billingsgazette.com or at 657-1387.