Snahapish River: Invasive Species Prevention and Control

The Snahapish River flows through a quintessentially northwestern Olympic Peninsula landscape characterized by dense forests, meandering waterways, and diverse fish and wildlife. Situated within the  Clearwater Corridor Natural Resources Conservation Area , the Snahapish is a vital artery in the coastal Queets watershed, contributing to the health of the region's ecosystems and supporting iconic Pacific Northwest species like chinook and coho salmon, steelhead, and cutthroat trout, as well as the Pacific lamprey. These species serve as an important nutrient pathway for local plant species, as well as a food source for many native animal species. The river's clear, cold waters and intact riparian forest are a testament to centuries of natural resilience in a dynamic and biodiverse region.

The Snahapish sub-watershed lies within the foothills of the Olympic Mountains on Washington's west Olympic Peninsula, flowing for a little over 10 miles through an old growth forested valley. It is a large tributary to the Clearwater River which flows into the Queets River before meeting the Pacific Ocean. The Snahapish plays a critical role in connecting the upland habitats of the west central Olympic Peninsula with downstream riparian and coastal ecosystems.

The region’s geomorphological history has also shaped the Snahapish into what it is today. Formed by volcanic, glacial, and hydrologic activity, the watershed is a mosaic of landscapes ranging from towering old-growth rainforest to forested wetlands and bogs, and gravel-bedded river corridors. These natural processes created the complex habitat beneficial to coldwater-reliant Pacific salmon and trout, while also supporting an array of wildlife like black bear, Roosevelt elk, river otter, beaver, osprey, American dipper, pileated woodpecker, belted kingfisher, among many other species.

The bear, elk, deer, otters, beaver, and birds stay away from the sounds of our work, but here are some of the other critters seen along the way during fieldwork in the Snahapish:

For over 10,000 years, the Snahapish River watershed has been a vital resource for the Quinault Nation and Hoh Tribe, who have built their traditions on its rich fisheries, fertile floodplains, and cultural significance. Traditional ecological knowledge shaped a deep connection to the land and water, fostering stewardship practices that maintained the river’s health for countless generations. Today, the watershed continues to hold cultural importance in local communities, highlighting the ongoing relationship between people and nature. The river continues to serve as a popular recreational fishing area and contributes to the Queets tribal fishery.

The recent history of the watershed reflects the challenges of modern land use. While the Clearwater NRCA Corridor is relatively intact, past landslide history from hillslope forestry and roads caused damage to the Clearwater River ( see resources at the end ). Nearby timber harvest and road activities continue and can present a variety of disturbances to the watershed and have introduced several invasive species to the area. Invasive plant species threaten to displace and outcompete native flora and fauna. To maintain biodiversity and ecosystem function, the 10,000 Years Institute (10KYI) has worked hard to protect the watershed through prevention of invasive species in the region, using proven restoration techniques and long-term monitoring to ensure the Snahapish River continues to thrive for future generations.

The lush coastal temperate rainforests of Washington State are some of the most ecologically rich environments on Earth, marked by towering conifers, dense understory vegetation, and abundant rainfall. This dynamic ecosystem provides critical habitats for Pacific salmon, steelhead, resident cutthroat trout, and countless other species. However, the coast's ecological resilience is increasingly threatened by invasive plant species which disrupt native ecosystems and diminish biodiversity. In the Snahapish watershed, addressing these threats is a cornerstone of long-term conservation.

Invasive species like Reed Canarygrass (RCG) have a competitive edge in these conditions, outcompeting native plants and altering hydrological and ecological processes in riparian environments (Schooler et al, 2006). RCG, an aquatic rhizomatous grass, forms dense monotypic stands in wetlands and along the edges of waterways, choking out native plants that provide habitat for both aquatic and terrestrial species. Left unchecked, it will exacerbate flooding, reduce water quality, and diminish the habitat complexity and food web vital for salmonid spawning and rearing.

A single RCG inflorescence (floret or seed head) can produce an average of 600 seeds (M. Tu, 2004). Sixty-five percent of these can remain viable after a year, and a small percentage can remain viable even after 20 years of burial (Grime et al., 1981, Toole et al., 1946). Continued, consistent mitigation, treatment, and removal actions are required in order to effectively curb the expansion of this species and others throughout watersheds such as the Snahapish. Seeds spread in high river flows are most commonly able to establish on moist patches of soil such as riparian buffers or areas that have been disturbed by construction or natural disturbances such as tree fall, river scour, and landslides (Galatowitsch et al., 1999). Unlike some invasive species, cutting, mowing, excavating, and other types of management are not effective means of controlling or removing RCG in riverine environments (Lavergne et al. 2010, 10KYI, 2021).

Surveying and identifying invasive species is the first step in restoration efforts. In the Snahapish watershed, repeated surveys are conducted to map the extent of infestations and track changes over time. These surveys are critical for understanding the spread of invasive plants, identifying areas of concern, and prioritizing treatment efforts. Detailed mapping allows 10KYI field crews to develop targeted strategies that allocate resources efficiently and effectively, ensuring the most critical areas receive timely intervention. In the case of RCG, repeated treatments over multiple years are generally necessary to completely control its growth and allow native plants the necessary time to reestablish. Follow-up monitoring and re-treatment ensures that these efforts lead to lasting ecological improvements, restoring natural processes that invasive species disrupt.

Data is collected in the field on a Survey123 form developed by and for 10KYI's invasives work, recording species, location, ownership, site characteristics, area covered, treatment information and more. The points and polygons are uploaded to GIS where data is used for planning fieldwork, documenting work accomplished, and applied in maps, reports, presentations and to communicate through outreach and dashboards.

10KYI crews utilize techniques including seed removal, manual pulling of very small clumps and selective herbicide application through targeted spray applications, which have proven to be particularly effective at controlling and preventing the spread of RCG.

Our methods are presented in the Protocol for the Prevention & Control of Reed Canarygrass, linked below. This protocol has been evolving since 2013 when we worked with the Quinault Natural Resources program where RCG was rapidly expanding in the Quinault watershed.

The stakes for invasion are particularly high in remote and dynamic coastal temperate rainforests like those surrounding the Snahapish River - where many areas are as yet unimpacted by non-native plant species. These ecosystems rely on a delicate interplay of soil, water, and plant communities, making them uniquely susceptible to the cascading effects brought on by the presence of invasive plants. Plant and animal species in the region rely on the varied and diverse habitats and food webs available throughout the watershed. Invasive plants arrest the regrowth of seedlings, saplings, and eventually large trees along riparian zones, which become large woody debris in riparian and stream channels in the process known as 'the large wood cycle', critical to upland, riparian, and aquatic ecosystem function. The loss of the complex riverine habitats formed by large wood and native plants degrades habitat quality and diversity within the watershed.

By tackling these challenges head-on, 10KYI's invasives projects protects the region’s biodiversity and supports the resilience of the Clearwater and Queets River corridors in the face of climate change and other natural and anthropogenic disturbances.

Invasive plants can be introduced to new locations in myriad ways. In this ecosystem, some of the most common vectors of invasive introduction are terrestrial and aquatic vehicle travel, human activity and footwear, logging activity and equipment, construction equipment and materials, boats and trailers, landslides, flood and high-water events, wind, as well as animal movement and activity.

In the case of RCG, the species was first identified in the Snahapish River in 2014, just downstream of the Clearwater Mainline. 10KYI staff was guiding a UW graduate student, Chris Vondrasek, who was interested in researching off-channel habitats through remote sensing and hydrologic modeling. We chose the Snahapish River as an undisturbed small river with side-channels. Upon observing RCG in the channel next to a very large fallen tree, staff investigated the channel and roads upstream of the mainline, and found a patch on the edge of a harvest unit in the ditch, apparently introduced in a roadside erosion control seed mixture. Since this detection, ​10KYI has surveyed all roads, and is continuing to control all RCG on roads in the watershed to prevent seed spread in ditches to the rivers.​

There are a variety of challenges to the field work conducted by 10KYI.

Invasive non-native plants such as RCG are inherently difficult to prevent and control - being tenacious, persistent, and aggressive. RCG can maintain viability even after prolonged submersion and is able to spread through rhizome ends known as tillers (Maurer et al., 2003). Combined with many seeds, sprouting nodes on the stems, and deep rhizomes that form vertical mats displacing water and other plants, tillers add to the species' competitive advantages over native plants, giving them the name of 'ecosystem engineer' (Corenblit et al., 2010).

Invasive plants pay no heed to land boundaries and property rights. Access can be difficult and at times impossible. If invasives establish on a parcel or land area that 10KYI does not have access to, it can lead to propagules and expansion of the invasive downstream - although, in the case of the Snahapish project, all landowners were supportive and provided access. At times, active timber harvest operations have affected scheduling and safe access.

Another issue is weather! The nature of these coastal temperate rainforests leads to frequent high flow events as a result of rainfall or snowmelt which make stream surveys impossible. High rainfall and flooding are always a possibility, and do not always match up to the seasons when the specific invasive plant treatment is most efficacious. The Snahapish also runs through two reaches of high canyons that are treacherous to get in and out of, sometimes requiring miles of additional hiking on slippery rocks to reach. To top it off, the rugged terrain, copious amounts of downed trees and large wood in the channels combined with thick understory in these critical biomes make this work challenging and time consuming. Our crews ROCK!

Funding for invasive plant treatment on the Snahapish River has come from a variety of sources since 2015. ​

Funding for invasive plant treatment on the Snahapish River has come from a variety of sources since 2015. The Snahapish project was initially funded through the  Washington Coast Restoration and Resiliency Initiative  in the Pulling Together Initiative (WCRRI  #15-1599 ). This is an ongoing restoration jobs program to prevent the spread of invasive plants at a regional scale in the coastal watersheds of the Olympia Peninsula.​

In 2021, fieldwork was funded through the  Salmon Recovery Funding Board  in the Snahapish River Invasive Plant Control grant (SRFB  #21-1117 ). The project's goal was to protect and restore aquatic and riparian habitats in the Snahapish, Clearwater, and Queets Rivers through the prevention and control of reed canarygrass (RCG) by surveying and treating 14 river miles of the Snahapish River's riparian and aquatic habitats. RCG from the Snahapish River was also prevented from moving into the Clearwater River at River Mile (RM) 19 and downstream to the Queets River at RM 7. Work in the Clearwater and Queets rivers has been conducted under the Pulling Together in Restoration program (WCRRI  #20-1416  &  #22-1313 ). River-adjacent roads were also surveyed and treated for all species to prevent migration in ditch and tributary flow to the Snahapish River.

If you are interested in learning more about the Snahapish, the importance of this ecosystem, and the impact of invasives, the following resources can provide additional information and learning.

 Clearwater Corridor Natural Resources Conservation Area | WA - DNR 

 Stream Catalog – WRIA 21 

​ Salmon Habitat Recovery Strategy – WRIA 21 ​​ 

 Snahapish River water quality data 

 Washington Coast Historic Steelhead Abundance 

 How logging road landslide siltation affects salmon and trout spawning in the Clearwater River basin 

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