Proposed reservoir above Seminoe could threaten world-class fishery, state and anglers say

A Utah-based hydroelectric company wants to build another reservoir above Seminoe Reservoir to produce bursts of energy when demand is high, promising to bring tax revenue and jobs to a rural part of central Wyoming. Fish and wildlife groups and the Wyoming Game and Fish Department, however, worry the project threatens the healthiest bighorn sheep herd in the state and the Miracle Mile, a world-class, blue-ribbon fishery. 

“I’m looking at this with a lot of caution, because waters with that quality of a fishery aren’t that common anywhere in the world,” said Matt Hahn, Game and Fish’s Casper fisheries supervisor. “Any activity that could jeopardize the quality and sustainability of the fishery, we should be pretty cognizant of and should proceed with caution on.”

The project would include a 13,400-acre-foot reservoir, a complicated tunnel system, new transmission lines, an underground powerhouse, and, at least during construction, two concrete mixing facilities. 

The company, called rPlus Energies, says the project could raise $60 million to $70 million in sales tax revenue, create up to 500 jobs during construction and provide $8 million to $9 million in annual property tax revenue and 35 full-time jobs during operation. Plans have been underway since 2019, and the latest round of public comment for the project’s permit through the Federal Energy Regulatory Commission ends Friday. 

Water as a battery

At its most basic, the Seminoe Pumped Storage project acts as energy storage. The company would use excess energy when production is high and demand is low to pump water uphill to fill a secondary reservoir where it would sit until energy is scarce and demand is high, at which point the water would rush down the tunnels through a power station and back into Seminoe Reservoir, generating up to 900 megawatts of power. As a comparison, the Dave Johnston Power plant east of Casper also produces 900 megawatts of power, albeit continuously. 

At its highest capacity, the system could generate power for up to 12 hours before requiring about 14 hours to refill. It could also produce less power for a longer period, said Lars Dorr, program manager for rPlus Energies. The concept is similar to lithium-ion batteries, only Matthew Shapiro, the company’s managing director of hydro strategy, says a pumped storage project can last up to 100 years and doesn’t degrade in its efficiency and capacity like batteries. 

“It provides a lot of flexibility to the grid to match what other generation sources are doing at that moment,” Shapiro said. “So that’s why it’s been a popular tool around the world for the past 100 years.”

Pumped storage projects were common across the country, used as a way to take excess coal or nuclear electricity generated, say, at night, and store it for peak daytime demand. They fell out of popularity, however, with the advent of more consistent natural gas energy. The last pumped storage project was built in 1995, and none exist in Wyoming. They’re finding favor once again as a way to take excess solar or wind energy and save it for high-demand periods and meet the growing need for power.

rPlus Hydro, the subsidiary in charge of the Seminoe project, formed in 2019 from a partnership between rPlus Energies and Gridflex Energy and has a dozen projects underway across the western U.S. and Kentucky. The Seminoe project would be one of its first, and it’s an ideal location because of its proximity to existing transmission and because there is already an existing reservoir, which means the company would not need to build two. 

Estimates show the project could run the company roughly $3 billion to build. Shapiro does not know if the energy would stay in Wyoming or leave the state as the company is still looking for potential buyers. 

Fish and wildlife concerns

Using Seminoe Reservoir as one of the two reservoirs in the system is more affordable. However, open-loop systems, as they’re called, come with the possibility for more environmental issues, according to a 2020 U.S. Department of Energy report.

Closed-loop pumped storage systems are often built away from primary waterways and run water back and forth between two reservoirs. Open-loop reservoirs, on the other hand, run water from an existing reservoir. That creates issues for what could be sucked up into the upper reservoir as well as the force of water coming back down into Seminoe itself.  

“The estimates of fish entrainment during pumping cycles, especially for walleye, could result in a loss of this wild fishery,” the Game and Fish Department wrote in formal comments about the project. 

Estimates from the company predict 5.21 walleye could be entrained in the system each hour, which Game and Fish estimates could be about 23,770 walleye per year, more than 5.7 times the annual catch rate by anglers.

The department’s biggest concern, however, is for the Miracle Mile, a stretch of water sometimes 15 miles long below Seminoe and Kortes dams that attracts thousands of anglers from around the world every year to catch trophy rainbow and brown trout. 

While only about 10,000 acre-feet would flow between the two reservoirs, and Seminoe Reservoir’s capacity is more than 1 million acre-feet, the second reservoir would remove water from, and dump water into, Seminoe Canyon. The canyon is a much narrower area, and 10,000-acre feet could be roughly the total volume of water in the canyon during dry periods, Game and Fish’s comments continued. 

In the peak of summer, lakes typically stratify, with cooler water on the bottom and warmer water on the top. Flushing water in and out of the canyon would create a “tidal-like ebb and flow of water” that would mix those water levels and “significantly increase the temperature” of water flowing out of Seminoe. 

Hahn and the Wyoming chapter of Trout Unlimited worry the project might threaten the viability of the Miracle Mile. The fishery exists because water flows from the bottom of Seminoe Reservoir at a consistent temperature throughout the year. Raise that temperature by a couple degrees, and the impact, especially in the summer on heat sensitive trout, could be dire. 

After Game and Fish submitted its comments, rPlus Hydro coordinated with Wyoming’s Department of Environmental Quality to run models showing there would be minimal impacts. 

Patrick Harrington, Wyoming Trout Unlimited’s government relations director, worries that if there are impacts such as temperature changes or water quality issues, they would be difficult, if not impossible, to mitigate. 

“How do you do adaptive management if you start to lose a fish population?” he asked. “How do you adaptively manage if something happens to the fishery and people can’t guide anymore?”

The fishing group held a recent informational session and about 90 people attended to learn what this could mean for the river.

But impacts extend beyond fishing. The site sits in the middle of the Ferris-Seminoe bighorn sheep herd’s winter range. The herd is also the only disease-free bighorn sheep population in the state, said Katie Cheesbrough, the Wyoming Wild Sheep Foundation’s executive director.

The project itself will cover about 1,000 acres of Bureau of Land Management and Bureau of Reclamation land. And while sheep can move around, Cheesbrough said five years of construction is a long time for bighorn sheep to be displaced by heavy traffic and dust. 

“There’s disturbance and then there’s chronic disturbance that displaces sheep from their habitat,” she said. “It’s not even about the food and habitat but about what a loss of food and habitat means for their susceptibility to disease.”

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Harrington and Cheesbrough ask anyone with thoughts to submit their comments to Federal Energy Regulatory Commission before public comment ends Friday. They hope FERC requires the company to complete a thorough environmental impact statement on the project, and Shapiro said he anticipates FERC will require one.

“The additional transparency of an EIS and additional processes with an EIS are what we’re after, so there’s an open public process to engage in the project,” said Harrington. “It keeps the conversation going.”

Shapiro and Dorr both encouraged people to reach out with questions and concerns. If approved, the company hopes to begin construction by 2027 and be operational by 2032.