Officials Eye ‘Gas Bubble Trauma’ Below Montana Dam

By Beacon Staff

HELENA – Montana officials are trying to determine if large releases of water at Canyon Ferry Dam near Helena are creating a harmful environment for fish that can lead to “gas bubble trauma.”

Officials say large releases at the dam the last two years have increased the amount of nitrogen and oxygen in the water that can cause fish kills. Smaller amounts of what’s called total dissolved gases can cause a fish’s eyes to bulge and form bubbles in fins.

“We were trying to find out how much total dissolved gas was in the water, so Fish, Wildlife and Parks could use that information to relate to what kind of impacts it may have on the fish,” said Bob Bukantis of the Department of Environmental Quality. “Also, if we have discussions with people who manage the dams, there might be some opportunities to use that information to adjust future dam operations.”

He said the state doesn’t normally monitor the gases but a strong spring runoff prompted the agency to start taking measurements. On Wednesday, the Bureau of Reclamation was releasing about 16,700 cubic feet per second of water from the dam.

Sampling earlier this month from below the dam found a level of total dissolved gases just below what can cause a fish die-off.

Montana was a plaintiff in a 2006 lawsuit against the U.S. Fish and Wildlife Service concerning gas bubble trauma, and some dams are now operated with gas bubble trauma in mind.

Bukantis said the problems faced by fish with gas bubble trauma is similar to that faced by scuba divers who rise too rapidly from deep water and get the bends. When ascending too fast, nitrogen comes out of the blood quickly and forms bubbles that can lead to strokes and heart attacks.

In fish, the nitrogen can cause bulging eyes and bubbled fins, as well as broken blood vessels that cause red spots.

“It can actually kill them it if gets too bad,” Bukantis said.

Fish that aren’t killed can be weakened and later die from other stresses.

“If the gas bubbles burst, that can lead to infections,” said Eric Roberts, a fisheries biologist with Fish, Wildlife and Parks. “Then if additional stresses like heat compound with other systemic types of problems, that leads to more mortalities. But we haven’t seen that below the dam.”

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