Floods churn Dolores into Sea of mud

Native fish survey canceled after mud kills fish

A capture net is hauled through the muddy Dolores River by a crew of environmental studies students from Western State Colorado University. The native fish survey earlier this month was canceled after flash floods made survey conditions extremely difficult.

Colorado Parks and Wildlife biologists Jim White and Harry Crockett prepare to catch native fish in the Dolores River. Heavy rains the day before built up a thick silt in the river, which killed many of the fish.

A flannelmouth sucker caught in the flood-churned Dolores River is held by a Parks and Wildlife researcher. The muddy water killed fish and left a film on skin, clothes and equipment.

SLICKROCK — A series of flash floods starting Aug. 21 on the lower Dolores River raised river levels an estimated 4,000 percent and churned a normally placid river into a sea of mud, killing an unknown number of native and endangered fish.

A team of fisheries biologists with Colorado Parks and Wildlife had begun a native fish survey Aug. 18 when the floods occurred on Aug. 20-21 and again Monday.

Heavy rains those days flooded Disappointment Creek, a Dolores tributary, bumping up the flow of the Dolores below Slickrock from a trickle of 11 cubic feet per second to 400 cfs overnight.

The survey is part of an effort to determine the health and habitat conditions of the bonytail chub, bluehead sucker and flannelmouth sucker.

Surveys done in the days prior to the flood found the river “a pearl necklace, characterized by deep pools, connected by a sliver of water, and then a deep pool again,” Parks and Wildlife researcher Paul Jones said on Aug. 21. “Today should be interesting.”

Harry Crockett, a Parks and Wildlife native fish species specialist, told the 13-person crew, each wearing a personal flotation device, the river is “in a flood stage right now, and that will make the survey more challenging. But we’re here, so we might as well give it a go.”

The crew was divided into two groups to capture, identify, measure and record fish in a three-mile section beginning at the Big Gypsum Valley boat launch.

As the researchers floated on the rush of muddy water, around them fish were rising to the surface, gasping and writhing.

“Their mouths (were) agape,” White said. “They’re trying to get air because they can’t absorb oxygen into their gills from the water. The silt is so thick it’s suffocating them.”

Soon hundreds of dead fish were seen floating, along with others apparently near death in the thick flows.

Team members were covered in a crust of mud that did not wash off. A hand dipped in the water came out covered in a thick, brown slime.

Researcher Paul White, covered with mud after being swept off his feet by the flows, hauled a long net to shore and looked through his collection of flood debris: plant mulch, wood, deer droppings, sand and mud.

Most of the inch-long bonytail chub in the net were dead. So were the young suckers and nonnative fish, including bullheads and smallmouth bass.

“They’ve evolved to handle murky waters, but these conditions are overwhelming them,” said Crockett, examining a dead chub. “You know it’s pretty bad if the bullheads are dying. I’ve never seen it this bad, and it is a serious concern. Now we have a better understanding of what they are going through during these heavy rain events.”

The few live fish were measured, identified and recorded. A GPS reading was taken of the location. The small fish were returned to the water, but researchers surmised the fish would not survive.

Some of the fish were kept for genetic analysis.

“We want to know if the native fish are specific to certain drainages and tributaries or are more wide ranging,” Jones said. “Genetics can help us get to that answer.”

Nonnative fish were discarded.

Researchers said the mud flows were due to a lack of flushing flows in the river below McPhee Reservoir.

The lower Dolores is dam-controlled from McPhee, and only a limited amount of water is allocated for the downstream fishery. The lack of regular flushing flows is causing an unnatural build-up of sand and sediment and is a threat to native fish and their habitat, according to Parks and Wildlife.

“The natural flush is important to regularly remove silt, so when there is a flash flood there is not so much of it,” White said. “We did not fully appreciate the build up (of sediment).”

The rest of the survey was canceled.

“We’re collecting more dead fish than alive,” Crockett said. “The nets are just trapping the mud in the water. It will be a challenge to analyze today’s data set, but we still learned something about the habitat conditions and what these fish go through when there is a flash-flood event.

“Flow management from the dam is a big part of a healthy fishery here.”


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