In 1990, Utah officials killed more than 99% of the fish in a 17,000-acre reservoir; years later, it became a top trout fishery

In August 1990, Utah wildlife officials launched a massive operation that involved chemically removing more than 99% of the fish biomass from Strawberry Reservoir in an attempt to rescue its collapsing trout fishery. The unprecedented project targeted millions of non-native fish that had disrupted the reservoir's food web and threatened its status as one of Utah's premier cold-water fishing destinations.

Why Utah officials decided to start over

The problem had been building for years. After Strawberry Reservoir was expanded in 1973, introduced Utah chub spread rapidly through the system. Redside shiners also became established, increasing competition for food.

By 1989, Utah chub accounted for more than 90% of the reservoir's total fish weight. The large population consumed plankton and competed with trout for limited food resources. Adult chub also preyed on young trout, making efforts to rebuild the trout population through conventional stocking increasingly ineffective.


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Wildlife biologists considered options including netting, commercial fishing and biological controls. However, none appeared capable of removing enough of the unwanted fish. Officials ultimately determined that a complete chemical treatment offered the most practical way to reset the reservoir's fish community.

A massive operation across the reservoir

The treatment covered the 17,000-acre reservoir as well as more than 170 miles of tributary streams connected to it. Officials first lowered the reservoir to its lowest operating level to reduce the amount of chemical required.

They then applied rotenone, a plant-derived chemical that interferes with cellular respiration in fish. Thousands of gallons of liquid rotenone and dry powder were distributed using barges, deep-water pumps, all-terrain vehicles, heavy equipment and aircraft.

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The operation also had to account for the complicated network of streams and waterways surrounding the reservoir. Dripper stations were placed along mountain streams so the chemical could reach side channels, springs, marshes and beaver ponds connected to the main system.

Within days, the treatment had spread throughout the targeted waterways, killing millions of Utah chub, redside shiners and other fish. Follow-up surveys found that more than 99% of the reservoir's fish biomass had been removed.

Officials rebuilt the fishery from scratch

The chemical was allowed to naturally break down after the treatment. By late autumn 1990, wildlife officials began the next phase of the project: rebuilding the fish population.

Millions of Bear Lake cutthroat trout were stocked along with sterile rainbow trout. The cutthroat trout were particularly important because adults become predators capable of feeding on smaller fish in open water.

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The idea was not simply to restore trout numbers but also to create a natural control mechanism for any Utah chub that survived the chemical treatment. With much less competition for food, the stocked cutthroat trout were able to grow rapidly.

Strawberry Reservoir makes a comeback

The strategy eventually produced the recovery officials had hoped for. By the mid-1990s, fishing records and wildlife surveys showed that the trout fishery had made a significant comeback.

State fishery data recorded annual catches of as many as 715,000 trout during peak years. Strawberry Reservoir again became a major destination for anglers, attracting more than one million angler hours annually during some periods and generating significant economic activity for the surrounding area.

The transformation was striking: a reservoir that had once been dominated by non-native fish had been reset and rebuilt around a trout population.

How officials protected the recovery

Utah wildlife officials did not stop after restocking the reservoir. Permanent fish traps and barriers were installed on important spawning streams, including the Strawberry River and Indian Creek.

These structures allow biologists to monitor spawning fish and prevent unwanted species from moving into upstream spawning areas. Fishing regulations and slot limits have also been used to protect mature, predatory cutthroat trout, which play an important role in keeping Utah chub numbers under control.

The Strawberry Reservoir project became a major example of large-scale freshwater management. Rather than trying to gradually control an overwhelming population of invasive or unwanted fish, officials essentially emptied the ecosystem of its fish biomass and rebuilt it with a carefully selected predator population.

More than three decades later, the 1990 operation remains a striking example of how aggressively wildlife managers can intervene when an aquatic ecosystem reaches a critical point—and how a near-total reset can be followed by a carefully managed recovery.