Fish kills blamed on winds, acidity

KLAMATH FALLS, Ore. – A new federal report blames ammonia, low acidity and low oxygen levels for fish die-offs in Upper Klamath Lake.

The report by the U.S. Geological Survey says the low oxygen levels may result from wind-driven currents. Affected fish include endangered Lost River and shortnose suckers.

It says the rapid growth and death of blue-green algae, decomposition of organic matter and warmer water also have contributed.

There have been no significant fish die-offs this year.

The report says the fast algae growth likely is caused by concentrations of phosphorus but that the reasons for the algae death is not known.

Algal blooms lower water acidity and often result in high ammonia levels, said Tamara Wood, the lead author.

Decomposition of the dead algae takes dissolved oxygen from the water, Wood said. Without sufficient oxygen, fish can die.

Oxygen-depleted water is carried from the southern part of the lake to the north, the preferred habitat of the endangered suckers.

Upper Klamath Lake has a generally clockwise circulation driven by prevailing northwesterly winds, Wood said.

Usually, lake water moves fast enough through the deepest parts of the lake to minimize the oxygen depletion caused by decomposition.

If the wind slows or changes, water with little or no dissolved oxygen can build up in the south. When this water goes north, suckers seek refuge and often end up crowded into areas near Pelican Bay, which can lead to large die-offs.