The 263 dead fish found scattered on the banks of Boulder Creek last month were killed by a combination of high temperatures and low water flows.
Sections of Boulder Creek were just a trickle on Aug. 20 — with water flowing by the Millennium Harvest House at only 1 cubic foot per second — because of high demand by area water uses. And the high temps pulled the oxygen out of the streamflow that was left.
From today’s Daily Camera:
Carol Ellinghouse, water resources coordinator for the city of Boulder, said a natural — but dramatic — decrease of about 20 cfs was measured in Boulder Creek’s flow at Boulder Falls on Aug. 20.
She called the drop an unusual “natural phenomenon” but couldn’t say specifically what might have caused it. Officials traveled upstream of Barker Dam in Nederland to see if there had been any illegal diversions of water but found none, she said.
Ellinghouse said the state water commissioner for Boulder Creek, who controls how much water is diverted by rights holders along the waterway, was unable to react quickly enough to the sudden drop in stream flow Aug. 20 to prevent the fish kill.
“It was a very dramatic drop,” she said. “He assumed there was a larger influx of water into the river.”
In Colorado’s Yamp River, 70 percent of all male bass now have female characteristics — a phenomenon called “intersex” — according to a new study released Monday by the U.S. Geologic Survey.
Intersex fish have been found in watershed across the country, including Boulder Creek.
The causes aren’t clear, scientists said in the report in Aquatic Toxicology. Nor could they say whether “intersex” fish could reproduce.
But the extent of the intersex fish was startling, said Jo Ellen Hinck, the USGS biologist who led the project.
“When we see 70 percent, we don’t think that’s normal,” Hinck said, referring to a sampling along the Yampa about 18 miles west of Craig.
Many scientists suspect that estrogen compounds — such as birth control and other pharmaceuticals — are to blame.