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A gently contoured backyard sweeping down to a glistening lake where fish jump and waterfowl nest and play- this is the scene many people in King County imagine when thinking about lakeside life. But if improperly tended, beautiful backyards like these can harm lake water quality and habitats. Lakeside dwellers can protect their lake by carefully planning and maintaining their yards and gardens.

Problems with soil and sediment

Transported by surface water runoff, sediment can wreak havoc on a lake's biological productivity. Sediment stresses and damages fish gills and cuts off sunlight that nourishes aquatic plants and animals. Pollutants (including metals and nutrients) can also adhere to these particles. Suspended in water, they can disturb the delicate balance of the lake ecosystem.

Where does this excess sediment come from? In undisturbed areas, rainfall is absorbed by the earth or filtered by vegetation before it can slowly enter a lake. But as people move in, they build roofs, driveways and other hard or impervious surfaces that prevent rain from soaking in. The water can no longer be absorbed, but flows faster, directly into the lake carrying sediment and pollutants with it.

This runoff water with its load of sediment, nutrients and other pollutants can be controlled by structural and non-structural or behavioral measures (called "best management practices" or BMPs) and by maintaining a buffer of native plants around the shoreline of a lake.

A buffer of native plants


Preserving a natural buffer of native plants is one of the best ways to protect a lake. Shoreline plants filter sediment and chemicals from runoff, provide food and shelter for fish and wildlife and can slow or prevent shoreline erosion. Shade from overhanging shrubs and trees can keep waters cool and oxygen-rich while limiting the growth of unwanted aquatic plants.

Established lake buffers are best left undisturbed. Even where a lake's natural plant cover has been removed or damaged, a buffer can usually be restored. An ideal buffer should be at least 20 feet wide, planted with an assortment of native trees, shrubs and ground covers. Paths or walkways to the lake should remain small so as to minimize shoreline impacts. A lake-friendly landscaper can suggest ways to optimize lake vistas while retaining shoreline vegetation. Low-cost native plants can be obtained from several local suppliers. A list of these native plant sources is available.

Keeping your lake chemical-free

Fertilizers and pesticides may provide a "quick fix" for lawns and gardens, but can have long-term impacts on the health of a lake. Both can be carried by wind and rain from lawns and gardens into lakes, with significant consequences for aquatic life. Reducing the use of pesticides protects lakes and contributes to a healthier environment for fish, wildlife and people. So instead of chemical pesticides, try a system of natural checks and balances to care for your lakeside plants:

  • Ask yourself whether you can live with some plant damage and whether destroying a pest is really necessary.
  • Use organic controls. Discourage pests with scattered borax; dishearten them with soap washes; destroy them with natural enemies like ladybugs or species-specific nematodes, both available at gardening stores. Consult Seattle Tilth Association 206-633-0451 or the Washington Toxics Coalition 206-632-1545 for additional alternatives.
  • Outwit pests by rotating crops and timing plantings to avoid peak insect invasions.
  • If pesticides cannot be avoided, choose the least lethal ones, and be sure they are not toxic to aquatic life. Never apply pesticides during windy weather or with-in 100 feet of a lake. Follow label directions and properly dispose of all hazardous waste at an appropriate collection site.

Chemical fertilizers, especially phosphorus, can stimulate plant growth in your yard as well as in the lake. Nutrients are all too easily washed from land surfaces into ditches and streams or directly into lakes, where they can feed aquatic plants and cause nuisance algal blooms. Organic fertilizers such as composted animal manure, commercially prepared organic soil additives or composted food and garden waste will break down slowly and improve the make-up of garden soils. Composting also keeps garden wastes out of lakes and puts it to good use through recycling.

If you do fertilize the lawn, remember that less fertilizer more often is better than a single, large application. Apply plant or lawn fertilizers only when plants show a need- not because you are following a schedule.

Waterfowl: too much of a good thing?

In recent years, non-migratory ducks and geese have been living the good life, protected and encouraged by human development in King County. These waterfowl love to feed on the succulent grasses of well kept lawns. With few natural enemies to keep their numbers in balance, geese and ducks can overpopulate and become a nuisance. Large flocks can overgraze lawns, littering yards and docks with droppings and molted feathers. Their droppings pollute lakes with nutrients, and, to make matters worse, their intestines may contain a tiny parasite that can cause a condition known as "swimmer's itch."

Canada geese are protected by the International Migratory Bird Treaty Act and, therefore, should not be harmed. However, these and other waterfowl can be discouraged by deterrents such as two-foot-high fences, large helium balloons, scarecrows, streamers or reflectors. Because geese and ducks are attracted to lawns or domestic grass growing along lake shorelines, a buffer of natural vegetation between the water's edge and a homeowner's lawn will deter them. Most importantly, do not feed waterfowl and discourage others from feeding them as well. Additional information about waterfowl feeding is available from WLRD 206-477-4800.

Lakeside logic


Remove trash, old tires and other unnatural objects from the lake shore. Leave fallen logs, root masses and other wild "clutter" to help form natural habitats.

Keep cars and livestock away from the lake shore. Construct boardwalks and ramps that allow reasonable access to lakes without causing shoreline erosion.

Don't leave soil exposed and vulnerable to erosion. Cover any exposed soils with leaves, straw or other mulching materials. Ideally, the shoreline itself should be planted with native species, rather than bulkheaded with rocks or concrete. Native vegetation buffers provide good shoreline stability and offer refuge for beneficial insects, fish and wildlife.

Most large-scale shoreline projects require a shorelines permit from King County 206-296-6797 and a hydraulic permit from the Washington State Department of Fish and Wildlife 360-775-1311 in Olympia.

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