The massive die-off happened in mid-December at the 77-acre Sparks Marina, a former gravel pit along U.S. Interstate 80 just east of Reno. Scientists believe the lack of oxygen occurred after a week of unusually cold weather caused a sudden turnover of the lake, sending the warmer, oxygen-rich waters from the surface to the bottom.
The latest sampling by the Nevada Division of Environmental Protection, on Jan. 29, supports the contention that the lack of dissolved oxygen was the only force at play, said Chris Crookshanks, a fish biologist with the state Department of Wildlife.
"All the testing has shown nothing alarming and nothing out of the ordinary," he told the Reno Gazette-Journal ( http://tinyurl.com/mf4slyh).
For now plans to restock the marina with any fish remain on hold. Wildlife officials had planned on stocking the lake with another 26,000 trout and 4,000 catfish beginning late this month. Restocking can't occur until dissolved oxygen levels improve at all depths, Crookshanks said.
"It's all going to be 100 percent dependent on dissolved oxygen levels," Crookshanks said. "Once we have sufficient levels, we will start the process of rebuilding the fishery."
On Jan. 13, biologists found dissolved oxygen levels at all depths of the lake to be so low as to not be survivable by fish.
The new tests revealed dissolved oxygen levels in deeper waters were still lethal to fish, but levels at the surface and down to a few feet were improving, Crookshanks said Tuesday.
"It looks like it's slowly coming back," he said. "It's the first positive indicator that we've had."
Michael Drinkwater, manager of the Truckee Meadows Wastewater Reclamation Facility, said the latest tests for toxicity involved placing fish in water drawn from the marina and measuring mortality and changes in reproduction.
"It came back nontoxic," he said. "It lends credibility to the working theory that oxygen depletion was the cause. It was not a toxic event. The fish just couldn't breathe."
Information from: Reno Gazette-Journal, http://www.rgj.com