Measuring the Pulse of the Upper Deschutes: 2025 Fisheries Monitoring Update

By Maggie Anderson, DRC Project Manager

The 2025 Upper Deschutes River Mitigation and Enhancement (M&E) Annual Report marks a significant step forward in how ODFW monitors this highly managed river system. Biologist Ben Stout and his team upgraded their approach—deploying a mark-recapture design for the first time—to generate more rigorous trout abundance estimates. Combined with continued tracking of spawning activity, juvenile trout, macroinvertebrates, water temperature, and newly initiated off-channel habitat sampling, this year's report offers the most comprehensive snapshot yet of where the river stands.

Why This Monitoring Matters

The M&E program was jointly funded this year by the Central Oregon Irrigation District(COID) hydropower mitigation fund and an Oregon Watershed Enhancement Board (OWEB) monitoring grant obtained in partnership with the Upper Deschutes Watershed Council. The central purpose of the fund is to implement restoration projects to mitigate hydropower impacts. Additionally, some funds are allocated to help with monitoring to document how aquatic life in the Upper Deschutes responds to ongoing changes in water management. The river's hydrology has been profoundly altered since Crane Prairie and Wickiup Reservoirs were built in 1922 and 1949. What was once an exceptionally stable, spring-fed river flowing at roughly 756 cfs year-round now swings between high summer flows of 1,400–1,600 cfs during irrigation season and minimum winter releases hovering around 100 cfs.

The Deschutes Basin Habitat Conservation Plan (DBHCP) is gradually changing that. Minimum winter flows are currently set at 100 cfs (years 1–7), with targets of300 cfs starting in 2028 and eventually 400–500 cfs by the 2030s. Each year of monitoring builds the baseline needed to evaluate whether and how those improvements are translating into ecological gains.

A Better Water Year—and What That Means for Fish

One of the most notable developments in 2025 was the improved water storage in Wickiup Reservoir. After years of near-complete drawdowns—the reservoir dropped to just 1.3-1.4% capacity in 2018, 2020, and 2021—storage at the end of the 2025 irrigation season reached 33%, or roughly 66,000 acre-feet.

Kokanee, largely absent from river sampling since 2021 (when the reservoir was drained), were captured again in 2025 despite the improved water carryover. Non-native species including Brown Bullhead, Tui Chub, and Threespine Stickleback—all with source populations in the reservoirs—continue to show up in annual sampling, underscoring the ongoing challenge of managing reservoir connectivity.

Trout Abundance: A Productive Tailwater

For the first time, ODFW used a mark-recapture approach across two one-mile reaches to generate statistically robust abundance estimates. The Wickiup Reach—immediately below the dam—and the Bull Bend Reach, several miles downstream, show the differences two river sections can have.

The Wickiup tailwater proved to be a highly productive stretch. Combined Brown Trout and Redband Trout abundance was estimated at 1,192 fish per mile, with a standing stock biomass of 162 kg per hectare. That figure is comparable to well-known tailwater fisheries like the Crooked River below Bowman Dam (172 kg/ha in2025), despite the Wickiup reach being unstocked. In other words, native production alone is sustaining a strong fishery in its current state—a sign of what careful flow restoration could unlock further.

The Bull Bend Reach showed lower overall abundance at 803 fish per mile and a biomass of 63 kg/ha, but had notably more juvenile fish of both species—suggesting this section is serving as important juvenile rearing habitat.

Redband Trout

Redband Trout are the native subspecies here, and the 2025 data shows a clear contrast between the two reaches:

- Wickiup Reach: 451 Redband Trout per mile, with an average length of 278mm (~11 inches). Fish up to 600mm (nearly 24 inches) were recorded.Condition factor (Fulton's K) averaged 1.00—solidly in the "fair" range for salmonids.

- Bull Bend Reach: 333 Redband Trout per mile, average length just145mm (~5.7 inches), with no fish exceeding 500mm. K factor averaged 0.96.While smaller overall, this reach had nearly twice as many fish under 200mm, indicating strong juvenile recruitment.

- The pronounced size difference between reaches likely reflects the tail water effect—dam outflow delivers nutrients and stable temperatures that support faster growth and better condition in fish closest to the reservoir.

Brown Trout

Brown Trout remains the dominant species by abundance in both reaches, outnumbering Redband Trout at every sampling location. The species is thriving in this system, particularly in the productive tailwater:

- Wickiup Reach: 732 Brown Trout per mile, averaging 389mm (~15inches). Many fish in the 600–700mm range were captured. K factor averaged 1.02.

- Bull Bend Reach: 456 Brown Trout per mile, averaging 279mm (~11inches), with almost five times as many juveniles under 200mm compared to theWickiup Reach. K factor averaged 0.97.

- The high proportion of juveniles in Bull Bend across both species is an encouraging sign of successful natural reproduction, even in a reach with lower overall productivity.

Mountain Whitefish

Mountain Whitefish showed an interesting inverse pattern compared to trout. Despite the Wickiup Reach having three times as many juvenile whitefish (likely due to tailwater productivity), average size was actually larger in the Bull Bend Reach (258mm vs. 200mm). Condition factor was not significantly different between the two locations, hovering around 0.86–0.89—in the lower accept able range but consistent across sites.

Spawning Ground Surveys: Both Brown and Redband Active

Annual redd surveys track spawning nest counts for both species across three areas: the Deschutes River from Wickiup Dam to Tenino Boat Ramp, from Tenino to Wyeth BoatRamp, and along a 2.2-km reach of Fall River.

In 2025, redd counts rebounded from 2024 lows in most areas. Brown Trout redds continued to outnumber Redband Trout redds in most reaches by two to one or more. Redband Trout redd counts increased in both Deschutes River segments in 2025. On Fall River, both species saw slightly higher counts than 2024, though the multi-year trend for Fall River remains downward.

The persistent challenge for both species is flow timing. Brown Trout spawn infall, when flows are at their winter minimum of 100 cfs—leaving large areas of spawning gravel high and dry. Redband Trout spawn in spring as flows ramp up to irrigation levels near 1,000 cfs, which can physically displace redds and smother eggs with sediment. Planned increases to minimum winter flows in Phase 2 of the DBHCP (300 cfs, starting 2028) may help address both problems.

Young-of-the-Year Trout: Strong Juvenile LocationsEmerge

Stream-margin electrofishing for young-of-the-year (YOY) trout continued across 16 sites from near Wickiup Dam to Steelhead Falls, with three new sites added near the dam tailwater in 2025. Estimates ranged from 106 to 1,840 juvenile trout per river mile (one bank), with a mean of 870.

Consistent high-production areas included Folley Waters, both Steelhead Falls sites, Lava Island, and River Rim Park. New in 2025: sites nearest Wickiup Dam posted some of the highest juvenile counts for the entire river—likely a reflection of increased winter flows leading to greater wetted width in stream margins and lateral habitats.

As expected, Brown Trout juveniles (average 107mm) were larger than Redband Trout juveniles (average 86mm) across the study area, a result of Brown Trout's earlier fall spawning season giving their offspring a head start in growth.

Surface Water Temperatures: Spring-fed Refugia vs.Stressed Downstream Reaches

ODFW deployed 12 temperature loggers across the mainstem and key tributaries, tracking hourly water temperatures from April through August 2025. The results highlight a stark divide between the upper and lower portions of the managed river:

- Spring-fed tributaries (Fall River, Spring River): Remained cold throughout summer, with daily maximums of 59°F and 50°F respectively—well within optimal ranges for Redband Trout and even Bull Trout.

- Upper Deschutes above North Canal Dam: Moderate temperatures in the low-to-mid 60s°F, buffered by large water volume and cold tributary inputs.

- Below North Canal Dam (Odin Falls, Cline Falls, Twin Bridges): Temperatures climbed above the state criterion of 68°F for Redband Trout for over 20 days, reaching as high as 76°F at Odin Falls. The drastic flow reduction from 1,400+ cfs to 100–400 cfs at the dam's diversion point strips the river of thermal mass.

- Steelhead Falls: A notable exception—cold spring inputs at Folley Waters bring temperatures back below the Redband Trout threshold, offering a thermal refuge downstream of the most stressed section.

Mountain Whitefish and the historically present Bull Trout have even lower temperature tolerances, making most of the Middle Deschutes currently unsuitable for those species during summer months.

Off-Channel Habitats: A New Frontier forMonitoring

One of the most significant additions to the 2025 program was the launch of off-channel habitat monitoring. Six sites between LaPine State Park and Sunriver were sampled in spring and summer to characterize fish assemblages, macroinvertebrate communities, and thermal regimes in oxbows, sloughs, side channels, alcoves, and percolation channels.

This work is especially important given the DBHCP's predicted outcomes: higher minimum winter flows are expected to increase the frequency and duration of connectivity between the mainstem and these off-channel habitats—areas that are critical for Oregon Spotted Frog, juvenile fish rearing, and native species recovery. An additional six sites between Sunriver and Bend will be added in 2026. Results will be incorporated into future annual reports.

Macroinvertebrates: Building the Baseline

Benthic macroinvertebrate sampling continued at 19 established sites from Wickiup Dam to Steelhead Falls and in three tributaries. Samples are collected in late summer/early fall, and processing for 2025 is partially funded through the OWEB grant. Results from 2023, 2024, and 2025 remain pending due to funding constraints, but are expected to be reported on in 2026 — highlighting the need for sustained investment in this long-term baseline dataset. Macroinvertebrates serve as both water quality indicators and a measure of forage availability for fish—a critical link in the food web as flow restoration proceeds.

Looking Ahead to 2026

The 2026 work plan continues all core monitoring tasks and expands the OWEB-funded components:

- Trout mark-recapture abundance estimates in the same two reaches

- Scale aging to develop length-at-age and growth rate data for Redband and Brown Trout

- Off-channel habitat fish use, macroinvertebrate, and temperature monitoring for six new sites between Sunriver and Bend

- Support for a fish salvage associated with repairs to the COID intake facility

Conclusion

The 2025 M&E Report shows a river in transition. Increased winter releases are helping balance irrigation demands with the river’s natural flow regime and mark-recapture data show promising fish populations.  Planned flow increases should continue to benefit these populations. At the same time, altered flow timing continues to limit spawning success and worsen summer thermal conditions, especially below North Canal Dam downstream of Bend

Five years of consistent monitoring is now yielding spatial and temporal patterns that were previously invisible. As minimum winter flows increase through DBHCP phases, this growing dataset will be essential for determining whether restoration measures are delivering measurable benefits to the Deschutes River's native fish communities.