Water stargrass: Difference between revisions
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'''Hand''' | '''Hand''' | ||
The most effective approach to manage stargrass is to remove the plant material at the roots. A small hand pulling effort has been tried over the last decade, but the effort would needed to | The most effective approach to manage stargrass is to remove the plant material at the roots. A small hand pulling effort has been tried over the last decade, but the effort would needed to be ramped up considerably to make an improvement. | ||
'''Mechanical''' | '''Mechanical''' | ||
Mechanical harvesting began in 2021. With approximately 16 acres harvested in 2024. The focus of removal locations has been in the Yakima Delta area, | Mechanical harvesting began in 2021. With approximately 16 acres harvested in 2024. The focus of removal locations has been in the Yakima Delta area, the Wanawish Dam pool, and Prosser Dam pool. A mechanical harvester reaches to a depth of about 3 feet and harvest would need to occur multiple times during the summer. | ||
'''Herbicides''' | '''Herbicides''' | ||
Revision as of 13:25, 28 August 2025
Overview and Concerns
Water stargrass (Heteranthera dubia) is a species of perennial aquatic plant in the Pontederiaceae family. It lives in freshwater such as lakes, rivers, and irrigation canals; preferring calmer waters. In the Lower Yakima River, water stargrass is prolific in many stretches of the lower 47 miles, below Prosser Diversion Dam. Water stargrass forms a bank to bank monoculture and can grow from stream bottom to the water surface and then continue growing horizontally forming a canopy at the water surface. It also forms dense vegetative mats over stream substrates covering gravels cobbles.
Water stargrass causes a suite of issues including:
- River displacement from total volume of water stargrass
- Increased sedimentation from reduced streamflow
- Changes to bottom substrates and gravel quality that reduce salmonid spawning habitat
- Changes to fish migration
- Changes in water quality including fluctuations in dissolved oxygen levels and pH from stargrass respiration and photosynthesis
- Plugged or or block irrigation screens and fish ladders
- Reduced recreation opportunities and challenges to boating and fishing
Studies
Multiple studies have been completed or are on-going on stargrass and the Lower Yakima River.
A 2009 report[1] by the USGS and Benton Conservation District detailed a 2004-2007 assessment of eutrophication in the lower 116 miles of the Yakima River. This was one of the first studies that characterized the proliferation of water stargrass in the Lower Yakima River. See PDF
A 2011 assessment of the Lower Yakima River includes a chapter on water stargrass[2]. See PDF
A 2020 Master's Thesis on water stargrass in the Lower Yakima River[3]. See PDF
The USGS and Benton Conservation District released a 2025 draft report on stargrass and water quality in the Lower Yakima River from 2018-2020 See PDF. The data is available on the USGS website, link.
Stargrass Control Efforts
In the last few years Benton County Conservation District has ramped up efforts to control water stargrass in the Lower Yakima River.
Hand
The most effective approach to manage stargrass is to remove the plant material at the roots. A small hand pulling effort has been tried over the last decade, but the effort would needed to be ramped up considerably to make an improvement.
Mechanical
Mechanical harvesting began in 2021. With approximately 16 acres harvested in 2024. The focus of removal locations has been in the Yakima Delta area, the Wanawish Dam pool, and Prosser Dam pool. A mechanical harvester reaches to a depth of about 3 feet and harvest would need to occur multiple times during the summer.
Herbicides
Potential aquatic herbicide treatments are being assessed.
Management and Control Techniques for Water Stargrass in the Lower Yakima River. Benton Conservation District. 2021[4]. Link
Websites
Benton Conservation District - Water Stargrass Management. Link
Mid-Columbia Fisheries Enhancement Group - Water Stargrass. Link
State of Washington Water Research Center Spring 2025 Seminar Series- Water Stargrass Video YouTube Link
Citations
- ↑ Wise, D. R., M. Zuroske, K. D. Carpenter, and R. L. Kiesling. 2009. Assessment of Eutrophication in the Lower Yakima River Basin, Washington 2004-07. Page 108. U.S. Geological Survey, Investigations Report 2009–5078.
- ↑ Appel, M., R. Little, H. Wendt, and M. Nielson. 2011. Assessment of the Lower Yakima River in Benton County, Washington. Page 182. Benton Conservation District.
- ↑ Pelly, A. C. 2020. Overabundant macrophyte growth alters ecosystem function in a lowland river. Washington State University.
- ↑ Pelly, A., M. Appel, and R. Little. 2021. Management and Control Techniques for Water Stargrass in the Lower Yakima River. Benton Conservation District.