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 phosphorus
concentrations but that the reasons for the algae death is not known.
When it dies and decomposes, it uses up oxygen in the water.
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, according to Wood.
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 dieoffs.
