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Aquatic plants are necessary to a lake's well-being, but they can also grow out of control and disrupt nature's delicate balance. Guided by an integrated aquatic plant management plan tailored to the needs of a particular lake, lakeside residents can control unwanted plants to restore the balance.

Aquatic plants play a significant role in a lake's system of checks and balances. Native species, which evolved along with other plants and animals in the Northwest, offer many benefits for healthy lakes. Benefits include providing food and shelter for fish and wildlife, stabilizing shorelines, producing oxygen and keeping sediment in place. Native aquatic plants also add to the beauty of a lake.

Unwanted non-natives

Eurasian milfoil (Myriophyllum spicatum), purple loosestrife (Lythrum salicaria) and several other non-native aquatic plants have made their way to the wetlands and lakes of Washington from Europe and Asia. Sometimes travellers brought them on purpose; sometimes seeds or plant parts hitched rides on clothing or came along with other plant materials in the aquarium industry or nursery trades.

These non-native aquatic plants have no natural enemies. They aggressively run rampant through wetlands and lakes, quickly establishing themselves and crowding out native species.

Non-native species can cause a number of problems in lakes:

  • By crowding out species that provide quality food and shelter for aquatic life, they can restrict fish production and cause fish populations to become unhealthy or decline.
  • Plant masses can form large surface mats, which can entangle boaters and swimmers.
  • When they die back in the fall, their decaying parts can reduce oxygen levels, release nutrients and impart an unpleasant smell and taste to lake water. Furthermore nutrients from decaying aquatic plants are available for algal growth, causing additional water quality problems.

Both non-native and native aquatic plants can grow faster and denser than normal when too many nutrients enter a lake. These nutrients come from many sources: failing septic systems, runoff from fertilized lawns and gardens, animal wastes, and stormwater runoff and erosion from construction sites. Nutrients and soil from these sources help to enrich lake bottom sediments, providing "fertile ground" for aquatic plants. With all this extra plant food, aquatic plants can grow too rapidly and become a nuisance.

Control with caution

Because any alteration to the plant life of a lake may have dramatic consequences, the removal of aquatic plants-non-native or native-is carefully controlled. One or more of the following permits may be required before you take steps to control the nuisance plants in your lake:

  • Shoreline permit exemption from King County
  • A clearing permit or exemption from King County
  • Hydraulic Project Approval from the Washington State Department of Fish and Wildlife
  • Permission from your local fire district and the Puget Sound Air Pollution Control Agency to burn plants
  • Permission from the Washington State Department of Agriculture to bag and landfill plants.

Contact King County Water and Land Resources Division (WLRD) Lake Stewardship Program (206/296-6519) to learn which of these permits you will need and the steps to obtain them.

King County WLRD has a limited supply of rakes and weedcutters for community groups who have obtained any necessary permits for removing aquatic plants. Contact WLRD at 206-477-4800 to borrow these or other weed control tools.

The Washington State Department of Ecology has developed a step-by-step guidance manual for developing an Integrated Aquatic Plant Management Plan (IAPMP). The goals of such plans are to develop solutions that respect the beneficial uses and balance of life in the lake and the watershed, are affordable, and that really work. The process involves two phases-a problem/site description and a control strategies description. The lake community and interested parties within its watershed work together to obtain information about a lake, recommend specific methods of control, identify permit requirements and analyze project costs. For more information about this planning program, contact the Department of Ecology at 360-407-6562 in Olympia.

A Hands-On Approach

Removal by hand is the simplest, cheapest and most environmentally sensitive way to control nuisance aquatic plants. But the underlying causes for plant growth must be addressed, or plants will grow right back. Always remember to:

  • Remove the entire plant-roots and all.
  • Pick up all floating fragments from the water or shoreline so that they won't re-root.
  • Compost plant material, except for purple loosestrife, which should be burned or landfilled with permit approval. Purple loosestrife should never be included with green disposal or curbside pickup of yard waste.

Familiar Natives

bushy pondweed
yellow pond lilies
Bushy pondweed (Najas flexilis) grows on lake bottoms to depths of fifteen feet. A submergent plant, it lives under water, except for the flowers which stick up above the surface in the springtime. Yellow pond lilies (Nuphar lutea) live in shallow lake margins and other still waters, to depths of 10 or 12 feet. They are examples of rooted, floating-leaved plants.
Bladderworts (Utricularia spp.) float freely just below the surface in shallow water above mucky lake bottoms. These free-floating plants provide food and cover for fish. Cattails (Typha latifolia) are common marsh plants that can grow in up to two feet of water. These emergent plants sink their roots in the lake bottom but send their stems, leaves and flowers above the surface.


Aquatic Plants: Identification, Benefits and Management, available from King County Surface Water Management (206-477-4800; ask for publications).

A Citizen's Manual for Developing Integrated Aquatic Vegetation Management Plans, available from the Washington State Department of Ecology, 360-407-6562.

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For questions about lakes in King County, please contact or call the Water and Land Resources Division front desk at 206-477-4800.