Table Of ContentLake 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
Myriophyllum spicatum
6.0. Noxious Aquatic Weeds in Lake Sawyer ..................................................................................... 19
Iris pseudacorus
6.1 Eurasian Watermilfoil ( ) ............................................................... 19
Nymphaea odorata
6.2 Yellow Flag Iris ( ) ........................................................................................... 21
Polygonum cuspidatum
6.3 Fragrant Water Lily ( ) ............................................................................. 22
Typha angustifolia)
6.4 Japanese Knotweed ( ) ..................................................................... 23
6.5 Narrow Leaf Cattail ( .............................................................................. 24
Myriophyllum spicatum
7.0. Aquatic Plant Control Alternatives ............................................................................................... 25
7.1 Eurasian Watermilfoil ( ) ............................................................... 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
Iris pseudacorus
7.1.6 Recommended Treatments .................................................................................................... 35
7.2 Yellow Flag Iris ( ) ........................................................................................... 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
Nymphaea odorata
7.2.4 Recommended Treatments .................................................................................................... 36
7.3 Fragrant Water Lily ( ) ............................................................................. 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
Polygonum cuspidatum
7.3.5 Recommended treatment ....................................................................................................... 38
7.4 Japanese Knotweed ( ) ..................................................................... 38
7.4.1 Hand Pulling and Cutting ........................................................................................................ 38
7.4.2 Soil Barriers .................................................................................................................................. 38
7.4.3 Chemical Control ........................................................................................................................ 39
Typha angustifolia Typha x glauca
7.4.4 Recommended Treatment ...................................................................................................... 40
7.5 Narrow Leaf Cattail ( and ) ....................................... 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
Iris pseudacorus)
8.2.3 Monitoring .................................................................................................................................... 44
‒
8.3 Yellow Flag Iris ( ........................................................................................... 44
Nymphaea odorata
8.3.1 Year 1 5 ......................................................................................................................................... 44
8.4 Fragrant Water Lily ( ) ............................................................................. 44
‒
8.4.1 Initial Control (year 1) ............................................................................................................. 44
Polygonum cuspidatum)
8.4.2 Follow-up Control (years 2 5) ............................................................................................. 45
‒
8.5 Japanese Knotweed ( ..................................................................... 46
8.5.1 Year 1 5 ......................................................................................................................................... 46
King County Science and Technical Support Section iii February 2015
Lake Sawyer Integrated Aquatic Vegetation Management Plan
Typha angustifolia
8.6 Narrowleaf Cattail ( ) ................................................................................. 46
‒
8.6.1 Initial Control (year 1) ............................................................................................................. 46
8.7 Follow up Control (years 2 5) ................................................................................................... 46
9.0. Plan Elements, Costs and Funding ................................................................................................ 47
9.1 Cost of the Plan ................................................................................................................................ 48
9.1.1 Planning Costs ............................................................................................................................. 48
9.1.2 Capital Costs ................................................................................................................................. 48
9.1.3 Operational and Maintenance Costs ................................................................................... 48
9.2 Sources of Funding ......................................................................................................................... 48
9.2.1 Grants .............................................................................................................................................. 48
9.2.2 Matching Funds ........................................................................................................................... 49
9.2.3 Long-term Sustainability ......................................................................................................... 49
10.0. Monitoring, Evaluation and Implementation ........................................................................... 50
10.1 Monitoring ......................................................................................................................................... 50
10.2 Evaluation of the Plan ................................................................................................................... 50
10.3 Implementation ............................................................................................................................... 50
10.4 Implementation and Evaluation ................................................................................................ 51
11.0. Bibliography .......................................................................................................................................... 52
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Lake Sawyer Integrated Aquatic Vegetation Management Plan
Figures
Figure 1. Map of Lake Sawyer watershed .............................................................................................. 1
Figure 2. Lake Sawyer Bathymetric Map (X marks the maximum depth) ................................ 2
Figure 3. Lake Sawyer Watershed and Urban Growth Boundary ................................................ 7
Figure 4. Lake Sawyer Drainage Basins and City Boundaries .....................................................10
Figure 5. Soils map of the Lake Sawyer Watershed. (from Hart Crowser 1990) ................11
Figure 6. Lake Sawyer Wetlands and Creeks .....................................................................................12
Figure 7. Lake Sawyer Aquatic Plant Community 1994 ................................................................16
Figure 8. Lake Sawyer Eurasian Milfoil Locations (patch consists of 2 or more plants) ..21
Figure 9. Lake Sawyer Fragrant Water Lily Locations 2010 ........................................................23
Tables
a a
Table 1. Average Summer (June‒October) Trophic Parameters for Lake Sawyer.
Chl- =Chlorophyll- , TP=Total Phosphorus, and TSI=Trophic State Index. ......14
Table 2. Aquatic plants identified in Lake Sawyer, 1994-2012. Plant list based on an
August 1994 survey, supplemented by later surveys conducted by King
County staff. .................................................................................................................................17
Table 3. Summary of Management Alternatives .............................................................................27
Table 4. Table 4. Estimated Cost of Lake Sawyer IAVMP implementation. ..........................47
Appendices
Appendix A: Control Method Options
Appendix B: Best Management Practices
Appendix C: Herbicide Labels
King County Science and Technical Support Section v February 2015
Lake Sawyer Integrated Aquatic Vegetation Management Plan
EXECUTIVE SUMMARY
In 2012 the City of Black Diamond, with assistance from King County Department of
Natural Resources and Parks, applied for and received a Washington State Department of
Ecology Aquatic Weed Management Fund Grant. This grant was awarded to fund the
development of an Integrated Aquatic Vegetation Management Plan (IAVMP) for Lake
Sawyer, with the City providing the grant match. The City of Black Diamond and King
County entered into an interagency agreement for King County staff to develop the IAVMP
for Lake Sawyer, contained in this document.
Lake Sawyer is located within the city of Black Diamond in South Central King County. The
lake is home to five Washington State listed noxious weeds. Without proper management,
these invasive plants have the ability to create large monoculture stands that reduce
biodiversity, impact water quality, and reduce recreational uses on the lake. The IAVMP is
intended to provide a holistic approach for managing or eliminating these five weeds from
Lake Sawyer for long-term public benefit. Input to and review of the IAVMP was provided
by a resident advisory steering committee and by the general public at multiple public
meetings.
The five aquatic weeds in Lake Sawyer are Eurasian milfoil, yellow flag iris, fragrant water
lily, Japanese knotweed, and narrow leaf cattail.
Eurasian milfoil has been in the lake since at least 1976. Several aquatic plant surveys
identified Eurasian milfoil as the lake’s most dominant aquatic plant species, covering
much of the shallow regions of the lake, although more recent surveys from 2012 and 2013
documented Eurasian milfoil around the lake, but in moderate to low densities with a large
diversity of other plants also found.
In 2013, King County staff and a Washington State Department of Ecology aquatic plant
specialist found milfoil weevils present on the invasive milfoil plants. The weevils provide
biocontrol for Eurasian milfoil and have the ability to limit populations of the plants, often
keeping the density of the invasive plants below a nuisance level, and are the likely cause of
the reduced amount of Eurasian milfoil. The other noxious weeds in Lake Sawyer are found
around the lake in varying densities.
The IAVMP outlines a long-term and holistic course of action for controlling the five aquatic
weeds in Lake Sawyer that addresses community interests and concerns. This outline
consists of plant control options, cost estimates, and potential funding options to
implement the plan.
The plan has been approved by the Steering Committee, the City of Black Diamond, and the
Washington State Department of Ecology. Department of Ecology approval of the IAVMP
allows the City of Black Diamond to apply for Aquatic Species Management grants to
implement it. These grants require a funding match from the applicant and generally are
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Lake Sawyer Integrated Aquatic Vegetation Management Plan
awarded for the entirety of the plan. The long term success of invasive aquatic plant
management in Lake Sawyer is dependent on several conditions, including:
(1) involvement of the community, (2) the availability of funding to implement the plan,
and (3) the ability to use adaptive management to address unforeseen or changing
environmental conditions.
King County Science and Technical Support Section vii February 2015
Description:The City of Black Diamond and King County Department of Natural Resources and Parks' . Eurasian Watermilfoil (Myriophyllum spicatum) .
