Whitewater courses – such as Durango’s Whitewater Park at Santa Rita Park – are popular throughout the state, but there is contention around how they affect river health.
Whitewater advocates have anecdotally noticed more fishermen near whitewater rapids, and they are working on gathering data to show how the parks can benefit fish.
But Colorado Parks and Wildlife data show the parks degrade fish habitat and their ability to migrate upstream, said Jim White, a biologist with the department.
“Whitewater park features are not suitable fish habitat,” he said.
Human-made parks create fierce velocities that make it hard for fish to migrate over them. Fish must also battle a washing-machine effect in the human-made pools, he said.
The parks are also being built in or near towns, where whitewater rapids would be less likely to occur.
“By the time you get down to broader valleys ... they are not typically natural features,” he said.
However, engineers and advocates – including Scott Shipley who designed the improvements to Smelter Rapid – argue whitewater parks can be built to improve fish habitat, and Colorado Parks and Wildlife is basing its conclusion on limited studies.
“As far as hard science goes, there is very little hard science on the issue,” said Shane Sigle, with Riverwise Engineering.
Despite the disagreement, proponents on both sides are interested in compromises that help protect fish. Some 30 whitewater parks are operating across the state, and they are boosting tourism and driving local economies, according to professionals in the field.
Smelter Rapid in Durango is an example of such a compromise. It was not quality-fish habitat to begin with, so it made sense to build permanent structures in that section, White said.
Colorado Parks and Wildlife also supported the Whitewater Park, saying construction of the permanent features secured a recreational-water right that helps protect fish from low flows, he said.
The city already was maintaining Smelter Rapid for whitewater features prior to construction of the park. The Army Corps of Engineers anticipates the grouted structures will limit the disturbance from continued maintenance, said Kara Hellige, senior project manager for the corps.
In addition, the corps requires the city to monitor the stability of the structures and banks, water quality and the movement of sediment after construction.
The monitoring required at Smelter Rapid and other parks should help engineers better understand how human-made rapids impact rivers.
“Anything you put in the river is going to have an effect – adverse or beneficial,” she said. She could not yet comment on what data from the city show.
But, long-term monitoring of whitewater parks is becoming more of a trend, and monitoring will help identify if parks can cause adverse effects, she said.
At Smelter Rapid, the corps required rock along the banks to help prevent the river from widening at an unnatural rate.
When a river is shallow and wide, the water temperatures can be high and hurt trout.
Shipley also worked with Colorado Parks and Wildlife to design alternative routes for fish around the rapids and did not include a smooth center channel, a first in the industry.
“Up until then, every whitewater park had a very smooth channel in the middle,” he said; he is currently working on a new whitewater park for the St. Vrain River in Lyons.
The previous whitewater park in the St. Vrain was the site of Colorado Parks and Wildlife study that showed parks could present a barrier to fish trying to swim upstream.
A flood washed away the park, and Shipley hopes to design a more fish-friendly replacement and to collect data on its impact in cooperation with Colorado Parks and Wildlife.
Locally, the city has several more river structures outlined in the Animas River master plan, but White wants to make sure any new structure would not harm the fishery because it is already hurting.
“It’s declined significantly, it really has.” he said. “What we don’t know is what’s driving it.”
It is a fact local fisherman have noticed, although the river has maintained its gold-medal status, which is a mark of quality.
“You’re not finding the numbers, particularly of brown trout,” said Cole Glenn, a fishing guide and manager at The San Juan Angler.
Some factors that could be impacting fish include water-quality changes and higher water temperatures, White said.