Officials have figured out why hundreds of fish are dying near the American Falls Dam
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AMERICAN FALLS — State officials finally have the answer to the baffling question of why hundreds of fish have died in the Snake River just below the American Falls Dam.
Representatives from the Idaho Department of Fish and Game, the Idaho Department of Environmental Quality, and Idaho Power conclude the death of hundreds of trout, sturgeon, bass and perch is due to low oxygen levels in the water.
On Aug. 4, a Fish and Game officer responded to calls about the dead fish floating near the Vista Boat ramp, as well as a sulfur-like odor.
“Some of our fishery staff responded minutes after the call and were able to gather dissolved oxygen levels,” Regional Fisheries Manager David Teuscher told EastIdahoNews.com.
Fish and Game was able to record safe levels of oxygen in the water and left confused as to why so many fish were dead. It was after inspection of the data from sensors in the water answers came.
The low oxygen levels were recorded days earlier by Idaho Power at the powerhouse of the American Falls Dam. As the water enters the dam, measurements of temperature and dissolved oxygen are recorded.
On Aug. 2, water entering the dam showed extremely low levels of oxygen. Recorded levels showed a decrease from 5 mg/l to 0 mg/l. To give a comparison, trout need 3.5 mg/l minimum to live. Fish and Game officials say low oxygen levels are normal this time of year; however, the drastic change that occurred on Aug. 2 is uncommon.
Fish and Game says precautions are already in place to prevent such low levels of oxygen on the river below the dam. The monitoring system measures parameters like temperature and dissolved oxygen. When dissolved oxygen drops below a certain threshold, a blower in the dam kicks on to increase oxygen into the water going through the dam. If after 10 minutes the levels of dissolved oxygen is not at an appropriate level, a second blower turns on. If this system is not sufficient, water behind the dam is sent over the spillway, churning the water in a turbulent flow along with additional dissolved oxygen.
Officials say because of this system required by Idaho water quality standards, only a few hundred fish died instead of thousands. The system at the American Falls Dam was in full force with maximum water flow over the spillway just as the sensors recorded the low levels of dissolved oxygen.
The low levels of oxygen are naturally occurring during the summer months in reservoirs and lakes as warm water temperatures along the top do not mix well with the cooler temperatures in the bottom.
Because of this, the system in place at the American Falls Dam is required and usually does what it needs, keeping the oxygen levels at required amounts to sustain fish life.
Teuscher says they believe the oxygen levels dropping to zero so quickly is due to high winds pushing low oxygenated water into the intakes at the dam. Quick response from the system as well as reports from anglers is what he saved thousands of fish from being killed.
“We appreciate the anglers that call.The sooner we hear about it, we can respond,” Teuscher said.