For 51 days this spring and summer, water managers opened the spigots on McPhee Reservoir, sending millions of gallons of water down the Dolores River – a boon to fish, farmers and boaters.
During the last 20 years, only 10 years have been boatable. But this year was remarkable for the number of boating days after extreme drought conditions in 2018.
McPhee Reservoir started 2019 with one of the poorest water levels in its history, but extraordinary snowfall allowed the Dolores Water Conservancy District to fill the reservoir and release 135,000 acre-feet of water.
The high-flow days will benefit the ecology of the entire corridor, said Mike Preston, general manager of the district. The big releases occurred between Memorial Day weekend and the first week of July, with a short intermission after Memorial Day.
The district met with stakeholders, such as boaters and biologists, weekly to determine water management strategy, Preston said.
“So far, everybody is pretty happy,” he said.
The Dolores River Boating Advocates were pleased with the number of boating days. While it was not the longest season ever, it was a good run, said Sam Carter, program and outreach coordinator for the group.
“A longer season would be great, but given the constraint of ensuring McPhee is filled, this was a great season,” he said.
The high levels in the reservoir will allow the district to provide irrigators all the water they have rights to and hold over water in the reservoir for next season, Preston said. The releases from the reservoir will also have lasting benefits for native fish and trees along the river, experts said.
The high flows help maintain and improve habitat for three species of native fish: roundtail chub, bluehead sucker and flannelmouth sucker, said Jim White, aquatic biologist for Colorado Parks and Wildlife.
The bluehead and flannelmouth sucker populations are both depressed in the Dolores. Their populations have been hurt by non-native fish and changes in habitat because of the dam, he said.
“Big water helps shape habitat, so the fish can persist through the tougher times,” he said.
This summer, White said he may have observed benefits of the last big water year on the Dolores, which was in 2017. He was surveying fish in Slick Rock Canyon and found an abundance of young flannelmouth suckers possibly from 2017 or 2018, he said. Higher water helps support spawning.
High water years, like this one, can also help native fish by reducing the opportunity for the non-native smallmouth bass to reproduce, he said. The smallmouth bass prey on the native fish and occupy their habitat, he said.
White’s team spent three days this season removing bass from the Dolores, he said.
There is probably “zero chance” of eradicating the bass on the Dolores, he said. “The best you can do is manage them.”
The large amount of spring runoff released from McPhee also kept the water district from needing to tap into water set aside specifically for fish, Preston said. So now the same amount of water can be released over a shorter period of time, which will be beneficial for fish.
The high-water year will also have lasting benefits for trees, such as cottonwoods and willows, because it will recharge the groundwater in the floodplain, said Cynthia Dott, a biology professor at Fort Lewis College. Dott specializes in studying the floodplain forest habitat and has worked on the Dolores River with her students.
Rainwater does not provide enough water to recharge the water table, and when the table drops too low, it can hurt large cottonwoods, she said. But there should be plenty of groundwater for the trees to tap into next year, she said.
“They will have plenty of water to keep their feet wet,” she said.
The high flows were also traditionally needed to scour the banks of rivers and leave open, muddy areas for young cottonwood seedlings to get established, she said.
However, because there have been so many years of low flows on the Dolores, willows have established themselves along the banks and high flows now are not enough to rip them free, she said.
“It is a smaller river below the dam, and it’s a narrower floodplain,” Dott said.
Humans will likely have to create patches suitable for young cottonwoods to get established for them to thrive because the river corridor has been changed by the dam, she said.