An unplanned electrical disruption at Rainbow Dam near Great Falls last week will result in the loss of more than 500,000 trout from the Giant Springs Fish Hatchery.

At about 4 a.m. on May 12, the generating unit at Rainbow Dam tripped offline. The unplanned event caused a temporary loss of power at the dam and interrupted NorthWestern Energy’s ability to control and monitor the water elevation in the reservoir behind the dam. During a period of about 35 minutes, water levels in the reservoir increased by 18 inches (1.2 feet above full pool for the reservoir).

Montana Fish, Wildlife and Parks operates the hatchery and FWP staff found out about the event after arriving for work May 12. The river water had receded, but FWP’s measurements at the hatchery revealed the water had risen about one inch above the boards separating the raceways from the river.

Giant Springs Fish Hatchery is located upstream and adjacent to the Rainbow Dam reservoir. With no way to confirm Missouri River water didn’t enter the raceways, FWP officials must consider the more than 450,000 rainbow and 50,000 brook trout housed in the outside raceways infected. Most will be destroyed. About 20,000 will be put into the river immediately adjacent to the hatchery and 500 will go into the children’s fishing pond near the hatchery.

The inside raceways and tanks at the hatchery were not infected by river water.

“This is an extremely tough decision, but we felt the only course of action was to destroy the fish in the outside raceways,” said Eileen Ryce, FWP Hatchery Bureau Chief and acting Fisheries Division Administrator. “We take the health of our fisheries very seriously and our tolerance for risk to the public’s resource is very low.”

The Missouri River is known to be infected with whirling disease, a parasite that can be lethal to young trout. And though whirling disease is a concern, the unknown other pathogens that could be in the river water also made salvaging the trout problematic.

“More important than whirling disease is the overall exposure to the river water itself,” Ryce said. “This is a very unfortunate circumstance and the decision to euthanize these fish was not taken lightly. It affects our hatchery staff very deeply.”

Giant Springs, like other FWP hatcheries, is on a secure water system operating only on fish-free spring water. That ensures the water supply is free of fish pathogens.

“We don’t raise any trout on untreated river water because of the general disease concerns,” Ryce said.

Once the fish are destroyed and the raceways emptied, they’ll be disinfected and the hatchery will be back online.

FWP operates 12 hatcheries around the state and is also the licensing authority for Montana’s private fish hatcheries. It is agency policy not to transplant fish from infected hatcheries. Agency rules also prohibit private hatcheries that are under quarantine from planting fish in any water body.

The trout from Giant Springs were being raised for stocking efforts for reservoirs, lakes and ponds around Montana. The planned fish stocking will continue with trout from other state hatcheries and donations from hatcheries operated by the U.S. Fish and Wildlife Service.

“We’re able to spread the burden of replacing these fish around to our other hatcheries and we’re also fortunate to have hatchery partners to help us find ways to make up for this loss,” Ryce said. “We anticipate being able to fulfill most of our stocking plans for this year.”

NorthWestern Energy has a longstanding partnership with FWP and has worked closely with the agency since the unplanned event at Rainbow Dam. NorthWestern has agreed to share in the cost of disposing of the fish and the subsequent hatchery clean-up. The company will also work with FWP on the development of protective reservoir-level monitoring system for the hatchery.

NorthWestern is taking steps to improve the power feed system to Rainbow Dam. The company will develop a redundant reservoir-elevation monitoring system and establish a plan to provide early notification of future potential changes in water levels in the reservoir that could affect hatchery operations.

Rainbow Dam and its other Montana hydroelectric facilities operate under a Federal Energy Regulatory Commission (FERC) license and NorthWestern has notified FERC of the event. Along with the notification, NorthWestern outlined to FERC the corrective actions it will take to prevent reoccurrence.

“NorthWestern takes its hydro operations compliance responsibilities very seriously and is working to develop corrective actions to prevent reoccurrence of this Rainbow full-pool exceedance,” said Jon Jourdonnais, Leader, Hydropower License Compliance at NorthWestern Energy . “NorthWestern also considers Montana Fish, Wildlife and Parks to be an effective and valued state-wide partner on many mutually managed public river resource and recreational issues.”

Fact sheet for Giant Springs Fish Hatchery infection

• Montana Fish, Wildlife & Parks’ Giant Springs Fish Hatchery raises four genetic strains of rainbow trout, along with brook trout. These rainbow trout strains include Arlee, Eagle Lake, Arlee/Erwin, and Gerard.
• The hatchery is fed by water from Giant Springs, which is one of the largest natural springs in the country, producing about 150 million gallons of water each day. Like all FWP trout hatcheries, Giant Springs is on a secure water system, meaning it uses water only from Giant Springs in order to avoid disease.
• The hatchery has 24 outside raceways and 40 inside tanks. The outside raceways were the only ones at risk of contamination from the river water.
• FWP operates 12 fish hatcheries around the state. The hatchery system produces about 45 million warmwater and 8.4 million coldwater fish annually.
• The Missouri River system is known to be infected with whirling disease, a potential lethal parasite that primarily impacts young rainbow and cutthroat trout.
• Prior to the potential incursion of river water, Giant Springs was known to be whirling disease free.
• Break down of fish to be destroyed including where they were destined to be planted and how they will be replaced:
  • 72,000, Arlee Rainbow, 4 inches in length. These fish were destined primarily for waters in FWP region 4. We make up this loss with fish from other hatcheries.
  • 148,600 Arlee Rainbow, 7-8 inches in length. 100,000 of these were going to be planted in Hauser Reservoir. Biologists are looking at redistributing our rainbow trout plants for Canyon Ferry, Hauser and Holter Reservoirs. The three reservoirs combined are scheduled to receive 650,000 rainbows and now will likely receive 500,000 combined. The distribution is yet to be determined. How we will replace the remaining 48,600 Arlee Rainbows is still under consideration. 2,100 fish destined for ponds in FWP Region 3 can be canceled. 1,500 planned for Spring Meadow Lake may be replaced by brood station trout. 30,000 planned for Beaver Creek Reservoir and 15,000 for Bear Paw Reservoir, both in Region 6, are fall plants. We will be able to make up a portion of those plants, but not sure how much at this point.
  • 99,000 Eagle Lake Rainbow, 2-4 inches in length. These fish were destined for various waters in FWP Regions 1, 2 and 4. We have more than enough surplus from state and federal hatcheries to cover this.
  • 85,000 Eagle Lake Rainbow, 7-8 inches in length. 50,000 of these fish were for Hauser Reservoir and this is being addressed with the fish redistribution for the three reservoirs. This leaves 35,000 for fall plants out of the Chouteau District, 20,000 for Pishkun Reservoir and 15,000 for Willow Creek Reservoir.  We should have enough fish for these plants from the healthy trout still at the Giant Springs Hatchery that we’ll bring outside once the raceways are disinfected.
  • 28,500 Arlee/Erwin Rainbow, 7-8 inches in length. 15,000 were for McGregor Lake which will now get 11,000, 7-inche Arlee Rainbow from the Bluewater Springs Hatchery.  2,300 are for ponds in FWP Region 3 that will be canceled. 4,000 were for the Milk River, which may be canceled and the rest were for various ponds. Hopefully brood stations will have some big fish for these ponds.
  • 50,000 brook trout for Georgetown Lake. 15,000 are coming from the Flathead Lake Salmon Hatchery to make up for part of that loss.
  • FWP will receive 100,000 rainbows from the U.S. Fish and Wildlife Service hatchery in Creston and is currently in conversations with FWS hatchery in Ennis for more fish. We are grateful for these partnerships.