Longmont-area wildlife officials hoping to improve St. Vrain fish passage with irrigation tweaks

Farmers and Longmont have relied on ditches fed by the St. Vrain River for water supply for more than a century. But they have restricted connectivity of habitat along the St. Vrain, especially for smaller fish unable to get over diversion dams of even moderate height to get back upstream.

Federal and local agencies are now working to renovate the water diversion infrastructure at several points along the stream between Lyons and Longmont to allow for better fish access from its urban section into the upper reaches of St. Vrain.

Grades vary by section

On its stretch from Lyons to Airport Road in Longmont, the St. Vrain in 2018 received low a grade — an F-plus — from Colorado Parks and Wildlife officials for its species counts. The stream from Airport Road and its junctions with Left Hand and Boulder creeks have fared better since the 2013 flood, receiving C-plus and B grades, respectively, according to .

An example of a smaller fish whose movement is hindered is the plains topminnow, which is considered “of greatest conservation need” and Colorado Parks and Wildlife is closely tracking its numbers in the stream.

“The ranges of these species have contracted over the decades diversion by diversion,” Boulder County Wildlife Biologist Tim Shafer said. “The last stronghold for them is the reach in the city of Longmont. That‘s putting all your eggs in one basket.”

If populations in one section of the stream were to suffer, it‘s important to have populations upstream so they can be recolonized below, Shafer said.

Boulder County officials are now negotiating with owners of the Niwot Ditch west of Longmont to rework the diversion dam‘s structure there, which was rebuilt after it was damaged in the 2013 flood. The rebuild includes some elements for easy fish passage, but it is only realistically usable by larger species such as trout.

“It‘s probably about 8 to 10 feet tall, depending on where you‘re standing,” Shafer said. “It‘s a fairly significant drop. … These type of fish passage designs don‘t work for the species of concern in the St. Vrain Creek. The goal is really to reconstruct that diversion with a more progressive design that will better accommodate those species.”

Improvements in progress

The diversion infrastructure causing the biggest contrast in fish populations from one stretch of river to the other is in Golden Ponds Park at the Beckwith Ditch, one of Longmont‘s oldest water rights holdings. Boulder County also is working with U.S. Fish and Wildlife officials to get a plan in place to ease fish access from downstream of Beckwith to the upper reaches of the river.

At the Bonus Ditch diversion near Martin Street in east Longmont, fish passage at the irrigation canal has already been improved as part of the Resilient St. Vrain project to shrink the river‘s floodplain through the city. Crews also are in the process of completing a pump station at the diversion.

“We have been able to overcome that barrier and allow diversion by incorporating nine smaller drop-structures … and incorporating fish passage in each of those structures,” Longmont Land Program Administrator Dan Wolford said of Bonus Ditch.

The plan is to wait to rebuild the Beckwith Ditch diversion until Resilient St. Vrain work in the western stretch of the city is funded with federal and state assistance, so the ditch work can be included with the river channel changes. That section of river is slated to be worked on last on the Resilient St. Vrain project timeline. There is not yet a date for when that work will begin or be completed.

“It will be interesting to see how (fish population) numbers do over the next three to five years with the construction of the Resilient St. Vrain project through town,” Wolford said. “We will be working with Colorado Parks and Wildlife over that time to monitor those conditions and numbers.”

Longmont Environmental Specialist Kevin Boden said the pace of flow through the river also needs to be slow enough to allow smaller fish species to swim upstream, in addition to installing passable infrastructure.

“These fish can‘t swim up a big current,” Boden said. “There has been a lot of research done with Colorado State University to figure out how much these fish can actually handle.”

Altering the current also is part of the Resilient St. Vrain project.

Ag, wildlife goals compatible

A design that would provide easier navigation for fish in the Niwot Ditch has been developed by the county in partnership with the U.S. Fish and Wildlife Service, Shafer said, but officials are awaiting approval from the ditch company, which has the final say over any proposed changes.

“They don‘t have to do anything,” Shafer said, as ditch owners‘ water rights trump fish conservation needs. “But they have demonstrated that they care about the creek. They would love to see fish passage work. They‘ve been very cautious to make sure they‘re not going to be injured in terms of water rights.”

There has been no commitment from the Niwot Ditch Co. so far to proceed, and the county is still in talks with the company about the final design.

Farmers using ditches targeted for fish-friendly renovations also are invested in maintaining the St. Vrain as a vital riparian habitat, and their need for crop water isn‘t necessarily at odds with the initiative to boost fish populations in the upper St. Vrain, Shafer said.

“The design we‘re proposing doesn‘t look like the more conventional design they‘re used to seeing over the decades up and down the stream,” he said. “We‘re getting them more comfortable with a progressive design. … In working with some of the farmers and water users in the basin, they‘re also the ones who grew up here. They‘ve seen the creek degrade over time. Their livelihoods depend on getting that water, but they would also like to see the creek in a better place than it is right now, a little healthier than they‘ve seen in the past decade.”

But bringing one ditch diversion up to modern fish passage standards won‘t be enough — a series of clearance is needed to repopulate the upper St. Vrain.

“We‘re starting to think on a watershed level,” Shafer said. “Getting one diversion done is one project out of many you really need to tackle.”

St. Vrain comparatively healthy

Despite the concerns over habitat connectivity and the resulting lack of fish from Lyons to Longmont, the St. Vrain‘s 2016 report card from Colorado Parks and Wildlife compares favorably with those of other Front Range streams — namely the Poudre, which was graded a C-minus and a D on its urban and plains reaches, respectively, while the St. Vrain received a B-minus and a B.

“The St. Vrain is our star performer,” Colorado Parks and Wildlife Native Aquatic Species Biologist Boyd Wright said.

He explained the three species native to the St. Vrain of greatest conservation need are the plains topminnow, the stonecat and the common shiner, which has not been documented in the stream since the 2013 flood.

Non-native species of concern include the largemouth bass, which Wright noted have grown in population in the St. Vrain in recent years, providing an angling opportunity, but posing potential harm to river health as predators of some native fish.

“I think there is a big push within the state and the federal governments to see more fish passage in general throughout the Front Range on all these streams,” Boden said. “It is very reassuring that we do have a healthy stream because the last thing we want is to have endangered species, which would make it difficult to do anything in the stream.”

Receive News & Ratings Via Email - Enter your email address below to receive a concise daily summary of the latest news and analysts' ratings with MarketBeat.com's FREE daily email newsletter.