Colorado has listed 105 miles of the Dolores River between Slick Rock and the Utah state line as an impaired waterway because of high water temperature from chronic low flows.
The Water Quality Control Commission of the Colorado Department of Health and Environment ruled on the river's impairment status during a hearing in December.
The section on the Lower Dolores River is "considered impaired because the temperature was greater than standards adopted to protect aquatic life," said Meghan Trubee, media relations official with the Colorado Water Quality Control Commission. "We're mostly concerned about the fish and macro invertebrates."
Identifying impaired waterways is part of the state's legal obligation under section 303(d) of the U.S. Clean Water Act. It requires states to survey rivers and lakes and inform the Environmental Protection Agency of those that do not have adequate controls to meet water quality standards.
"Because the stream is listed as impaired, the division is responsible for developing a plan to address the temperature impairment known as total maximum daily load (TMDL)," Trubee said. "The segment will remain on the 303(d) list until a TMDL is developed and approved by the EPA."
A year's worth of temperature data from a water-quality station at Slick Rock showed the river went above the daily maximum temperature standard 10 times - five in September 2013 and five in June 2014.
The separate readings went above daily maximum standard for March to November of 28.6 Celsius, or 83 degrees Fahrenheit.
"Warmer water has less ability to hold dissolved oxygen, which fish need," said Jim White, a fish biologist with Colorado Parks and Wildlife. "The other reason is that higher base flows in the summer would create more habitat for growing invertebrates, the food relied on by native fish."
The impaired section is below McPhee dam and reservoir and has not had a recreational whitewater release since 2011.
Water allocated for fish habitat, about 31,796 acre-feet, is held in McPhee reservoir and released throughout every year. In the winter, flows below the dam are 20-30 cfs. During summer, they reach 60-80 cfs if there is no whitewater release.
A series of low snowpack years have left the reservoir below full and only able to supply irrigation demands. A whitewater release occurs when there is more runoff than the reservoir can hold.
The Dolores Water Conservancy objected to the lower Dolores impairment listing, but wasn't successful.
In an objection brief, DWCD argued that the weekly average temperatures did not exceed standards, that non-attainment by available water flow does not qualify for the 303(d) list, and that there was "questionable data" during testing periods, among other reasons.
The objection further states that "this (measuring) site is upstream of the confluence with the San Miguel River and other tributaries that add considerable flow and no doubt alter the temperature of the river."
jmimiaga@the-journal.com
