Two-year Review of Watson Lake Fish Ladder Indicates It Has Been a Success

Colorado Parks and Wildlife monitoring efforts of the fish ladder installed on the Cache la Poudre River at the Watson Lake State Wildlife Area two years ago shows it has been a success.

The fishway was designed to allow passage around a diversion structure in the river for multiple fish species. A partnership was formed between private and public entities to make it possible.

“Overall, we are happy with the project and have documented fish moving upstream and downstream in the structure,” said CPW Aquatic Biologist Kyle Battige. “The fish ladder has improved conditions on the river and reconnected over two miles of river habitat by providing upstream movement opportunities for fish that had not existed at the Watson Lake Diversion Structure location since it was built in the 1960s,” Kyle said.

Two separate Passive Integrated Transponder (PIT) tagging efforts helped CPW monitor fish movement up and down the river after the ladder was installed. CPW tagged 71 fish on April 26, 2019. They were released in the downstream half of the fishway for initial evaluation. Researchers with Colorado State University also tagged fish downstream of the fishway as a part of a larger movement study on April 4, 2019.

Data from the PIT tags documented successful upstream and downstream movement, with 41 of the 71 CPW tagged fish utilizing the ladder and 36 of those fish successfully ascending the entire structure. The other five fish were recorded on one of the other two operational antennas within the structure but not at the top antenna. Our detection data indicates that 51 percent of fish tagged by CPW successfully ascended the entire structure.

Additionally, eight brown trout tagged by CSU and released 50 meters or further downstream have been documented using the fishway.

“Documenting 51 percent of the CPW-tagged fish along with CSU- tagged fish utilizing the structure over the course of several months is exciting,” Kyle said. “The fish ladder is performing as designed and is allowing fish to move freely up and downstream through the reach as they want. Further evaluation is warranted to investigate movement success across a broader size range within each fish species, but to date, we have documented adult fish successfully navigating the fishway.”

Of the three fish-tagged species – longnose sucker, brown trout, and rainbow trout – at least one individual across all tagged species has successfully navigated the fishway.

Other areas monitored that indicate a successful project are measured water velocities in the fishway, discharge measurements in the fishway, and water delivery to the hatchery. The cone screen constructed above the fish ladder where water gets delivered to the hatchery prevented fish entrainment by screening water delivered to the hatchery. That has not clogged during the fall leaf seasons, decreasing CPW staff time spent cleaning old inlet infrastructure. The cone screen is powered by a solar panel and has benefited hatchery operations while not impacting water delivery.

To satisfy the measurement of Northern Water’s potential future augmentation flows from Glade Reservoir, the fishway was designed to carry up to 30 cubic feet per second (CFS) before spilling over the dam. Based on CPW measurements since construction was completed in the spring of 2019, the fishway more than meets that criteria, with its overall capacity being closer to 50 CFS.

Morning Fresh Dairy, one of the project partners, utilizes the structure to measure future water flows.

There was a seamless collaboration between public and private entities who came together to improve the river and its habitat. Along with CPW and Morning Fresh Dairy, noosa yoghurt, Northern Water, and Poudre Heritage Alliance, all were key partners in the project.

Learning lessons gleaned from this project that can be applied to help future ladder designs include careful consideration of tradeoffs between flow measurement and fish passage and minor design tweaks to optimize water velocities in fish ladders.