Dworshak Reservoir 2024-25 Fisheries Update

By Tyler Zumwalt

Dworshak Reservoir has provided great angling opportunities in 2024. Reports from anglers and research by Idaho Fish & Game showed that kokanee fishing was better than the previous two years and Smallmouth Bass continued to provide a world-class fishery. Additionally, Rainbow Trout stocking provided diverse opportunities for both boat and shore anglers.

Kokanee

The IDFG trawled Dworshak Reservoir for kokanee on July 29-31, 2024. The data from this survey allows us to understand how this year’s kokanee population compares to past years and what we could expect in the future. To fully understand how kokanee abundance and size compares to the past, we need to break down the data based on how old the kokanee are. Kokanee don’t live very long in Dworshak, with most only living for two years before they spawn and die. In years with high abundance of kokanee and slower growth, some of the kokanee will live for three years before they spawn. Age-2 and age-3 kokanee are the fish big enough for anglers to target and catch. Based on this year’s trawl data, age-2 and age-3 kokanee were larger than they’ve been in the last four years, but was similar to the 20-year average size of 10 inches (see below). Kokanee were large because the total abundance of kokanee decreased from the record-high abundances shown in 2020 and 2021. With decreased abundance, there is reduced competition for food and kokanee can grow to larger sizes.

Fewer age-1 kokanee (4 – 7 inches) were observed in 2024 trawling compared to the last four years and the 20-year average. The number of age-1 kokanee observed is an important indicator of how many will be available to anglers in 2025 as age-2 fish. Fewer age-1 kokanee in 2024 suggests there will be fewer available to anglers in 2025. Fewer kokanee, however, also means less competition for food and higher growth rates. Therefore, there may not be near as many age-2 kokanee next year, but we could potentially see some of the larger sized kokanee we have seen for some time. This “boom and bust” cycle of kokanee is common in Dworshak Reservoir (see figure below) and is believed to be influenced by changes in the size of spawners. 

Kokanee fry represent the youngest year class and are the juvenile kokanee hatched from 2023’s spawning adults. The number of kokanee fry (age-0) observed in 2024 trawling was well above the number observed over the last four years, as well as the 20-year average. Assuming normal survival, this strong year class could yield a high abundance of age-2 kokanee in 2026. Just how big these kokanee get will be dependent on their survival rates, as well as the abundance of the other age classes of kokanee in the reservoir at the time.

Smallmouth Bass

Smallmouth Bass electrofishing surveys in 2024 showed a similar amount of bass > 12 inches available to anglers, compared to those observed in 2022 and 2023. Trophy-sized Smallmouth continue to be caught in the reservoir, with 3-5 pound fish being a common occurrence at tournaments. We do, however, suspect growth rates of bass > 12 inches has likely declined this past year due to low numbers of age-1 kokanee in the reservoir. 

The number of juvenile Smallmouth Bass (<12 inches) observed in 2024 was higher than what’s been observed over the past two years. The increased number of juveniles suggests that the number of bass available to anglers in 2025 and 2026 is likely to be similar, if not higher than the number available in 2024. This increased number of bass, paired with a higher number of kokanee fry in 2024, may provide optimal conditions for increased growth of Smallmouth Bass in 2025.

Rainbow Trout

Rainbow Trout fishing in Dworshak reservoir is another fishing opportunity not to be overlooked. Roughly 10,000 12-inch Rainbow Trout are stocked from May through October at the Dent Acres boat launch, with a quarter of them stocked in October. With kokanee fishing slowing down, Rainbow Trout can provide an excellent fall fishing opportunity. Every year anglers report catching Rainbow Trout > 16 inches, with the occasional fish > 20 inches.

 As a reminder, current fishing regulations on Dworshak reservoir are set at 6 trout/day, 25 kokanee/day, and 6 Smallmouth Bass/day.