Lake Sawyer Integrated Aquatic Vegetation Management Plan King County, Washington February 2015 Alternate Formats Available Lake Sawyer Integrated Aquatic Vegetation Management Plan King County, Washington Prepared for: The City of Black Diamond Submitted by: King County Water and Land Resources Division Department of Natural Resources and Parks Funded in part by: The Washington State Department of Ecology Lake Sawyer Integrated Aquatic Vegetation Management Plan Acknowledgements The City of Black Diamond and King County Department of Natural Resources and Parks’ Water and Land Resources Division would like to thank the members of the Steering Committee for their help in the development of the lake Sawyer Integrated Aquatic Vegetation Management Plan. Additionally we would like to thank Jennifer Parsons and Lizbeth Seebacher from the Washington State Department of Ecology for their review and expertise in aquatic noxious weeds. Citation King County. 2015 Lake Sawyer Integrated Aquatic Vegetation Management Plan. Prepared by King County Freshwater Assessment Unit, Water and Land Resources Division. Seattle, Washington. King County Science and Technical Support Section i February 2015 Lake Sawyer Integrated Aquatic Vegetation Management Plan Table of Contents Executive Summary............................................................................................................................................. vi 1.0. Introduction .............................................................................................................................................. 1 2.0. Problem Statement ................................................................................................................................ 4 3.0. Management Goals ................................................................................................................................. 6 4.0. Community Involvement ..................................................................................................................... 8 4.1 Steering Committee, Outreach and Education ........................................................................ 8 5.0. Watershed and Waterbody Characteristics ................................................................................. 9 5.1 Drainage Basin .................................................................................................................................... 9 5.2 Geology and Soils ............................................................................................................................ 10 5.3 Streams, Wetlands, and Sensitive Areas ................................................................................ 12 5.4 Water Quality and Existing Management .............................................................................. 13 5.5 Characterization of Aquatic Plants ........................................................................................... 15 5.6 Fish ....................................................................................................................................................... 17 5.7 Beneficial and Recreational Uses .............................................................................................. 18 6.0. Noxious Aquatic Weeds in Lake Sawyer ..................................................................................... 19 6.1 Eurasian Watermilfoil (Myriophyllum spicatum) ............................................................... 19 6.2 Yellow Flag Iris (Iris pseudacorus) ........................................................................................... 21 6.3 Fragrant Water Lily (Nymphaea odorata) ............................................................................. 22 6.4 Japanese Knotweed (Polygonum cuspidatum) ..................................................................... 23 6.5 Narrow Leaf Cattail (Typha angustifolia) .............................................................................. 24 7.0. Aquatic Plant Control Alternatives ............................................................................................... 25 7.1 Eurasian Watermilfoil (Myriophyllum spicatum) ............................................................... 29 7.1.1 Hand Pulling and Cutting ........................................................................................................ 29 7.1.2 Diver Hand Pulling ..................................................................................................................... 29 7.1.3 Bottom Barriers .......................................................................................................................... 29 7.1.4 Chemical Control ........................................................................................................................ 30 7.1.5 Milfoil Weevils ............................................................................................................................. 30 7.1.6 Recommended Treatments .................................................................................................... 35 7.2 Yellow Flag Iris (Iris pseudacorus) ........................................................................................... 35 7.2.1 Hand Pulling or Cutting ........................................................................................................... 35 King County Science and Technical Support Section ii February 2015 Lake Sawyer Integrated Aquatic Vegetation Management Plan 7.2.2 Bottom Barriers .......................................................................................................................... 36 7.2.3 Chemical Control ........................................................................................................................ 36 7.2.4 Recommended Treatments .................................................................................................... 36 7.3 Fragrant Water Lily (Nymphaea odorata) ............................................................................. 36 7.3.1 Hand Pulling and Cutting ........................................................................................................ 36 7.3.2 Bottom Barriers .......................................................................................................................... 37 7.3.3 Sediment Agitation (Weed Rolling) .................................................................................... 37 7.3.4 Chemical Control ........................................................................................................................ 37 7.3.5 Recommended treatment ....................................................................................................... 38 7.4 Japanese Knotweed (Polygonum cuspidatum) ..................................................................... 38 7.4.1 Hand Pulling and Cutting ........................................................................................................ 38 7.4.2 Soil Barriers .................................................................................................................................. 38 7.4.3 Chemical Control ........................................................................................................................ 39 7.4.4 Recommended Treatment ...................................................................................................... 40 7.5 Narrow Leaf Cattail (Typha angustifolia and Typha x glauca) ....................................... 40 7.5.1 Hand Pulling and Cutting ........................................................................................................ 40 7.5.2 Bottom Barriers/Shading ....................................................................................................... 40 7.5.3 Chemical Control ........................................................................................................................ 40 7.5.4 Recommended Treatment ...................................................................................................... 41 8.0. Recommended treatment Plan ....................................................................................................... 42 8.1 Permits ................................................................................................................................................ 42 8.2 Eurasian Watermilfoil (Myriophyllum spicatum) .............................................................. 43 8.2.1 Initial Control (year 1) ............................................................................................................. 43 8.2.2 Follow-up Control (years 2‒5) ............................................................................................. 44 8.2.3 Monitoring .................................................................................................................................... 44 8.3 Yellow Flag Iris (Iris pseudacorus) ........................................................................................... 44 8.3.1 Year 1‒5 ......................................................................................................................................... 44 8.4 Fragrant Water Lily (Nymphaea odorata) ............................................................................. 44 8.4.1 Initial Control (year 1) ............................................................................................................. 44 8.4.2 Follow-up Control