Naches River FMO Habitat

Overview

The Naches River is the main tributary of the Yakima River entering just north of the city of Yakima. It begins approximately 45 miles upstream at the confluence of the Bumping and Little Naches rivers (the American River flows into the Bumping River about 3.5 miles above this point). Other major tributaries of the Naches River include the Tieton River and Rattlesnake Creek. With the exception of storage dams, which block upstream migration on the Bumping and Tieton rivers, bull trout are able to migrate freely within the system. Below these dams there are 16.5 miles of habitat available to fish on the Bumping River and 21 miles on the Tieton River. Numerous smaller tributary streams also flow into the Naches River.

The shared FMO habitat for all of the Naches River fluvial bull trout populations is considered to be primarily located in the Naches River although there is some evidence that the Tieton River and mainstem Yakima River are used as well. It is difficult to summarize habitat conditions in the Naches River given the length of the river (45 miles). Generally, the upper 27 miles (above the Tieton River confluence) flows through forested lands of mixed ownership. Much of this is National Forest but there are also areas that are privately owned; residences and groups of residences are ubiquitous with a few small farms present lower in the reach. There is also considerable recreational access and use. State Route (SR) 410 runs adjacent to the river for the entire length of this segment and has impacted floodplain function. Below the Tieton River confluence land use along the Naches River converts to predominantly agricultural (orchards, irrigated pasture, and hay production) and there are numerous water diversions. U.S. Highway 12 runs adjacent to the river from the Tieton River confluence downstream to the mouth impairing floodplain function. Haring (2001) describes numerous positive habitat attributes such as good riparian condition (in the upper portion of the river), good pool frequency and depth, good LWD and substantial amounts of off-channel habitat. These positive attributes combined with the length of river available for bull trout habitation suggest that FMO habitat conditions in the mainstem Naches River are not limiting population productivity for Naches River fluvial bull trout populations.

The significance of the Tieton River as FMO habitat for the Naches River fluvial populations is unknown. However, adult bull trout have been captured in the Tieton River (in the stilling basin directly below Tieton Dam) that genetically assigned to the Rattlesnake Creek and American River populations (Small et al. 2009). The Tieton River flows for just over 23 miles from the base of the dam to its confluence with the Naches River. U.S. Highway 12 parallels the river on the left bank for much of this length, which has altered the riparian corridor. However, this road has little effect on floodplain function as the river is naturally confined in this section. Other roads, structures, several developed campgrounds, and the Yakima-Tieton diversion dam contribute to the rivers disturbed condition. The channel is in poor condition due to structural restrictions and an almost complete absence of LWD (Haring 2001). The most significant negative impact on fish habitat in the Tieton River is the regulated flow regime, which also contributes to the lack of LWD and channel complexity. The timing and magnitude of stream discharge in the river is the most highly altered of any in the Yakima Basin. Winter flows are 60-80% less than would occur under unregulated conditions and flow variability is extremely low. At a time when overwintering bull trout would be seeking pool habitat with cover, relatively none exists. During the first week of September an extreme, managed hydrologic event (“flip-flop”) occurs when dam releases are rapidly increased and average river flows often exceed by an order of magnitude what would be a natural base flow, sometimes exceeding 2,000 cfs. This condition persists to varying degrees for over a month.