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The ways that invasive species move from one place to another, or pathways, may be natural or created by people. Natural pathways include things such as birds or wind, which carry seeds, or water, which carries species from river to ocean. Human-created pathways include things such as boat hulls, which carry species across an ocean or from lake to lake; car tires, which carry seeds; and humans who plant wildflower seeds from another state in Washington, or dump their aquariums in creeks behind their houses. It is these human-made pathways that we can do something about. Knowing what they are is the first step to finding a solution.

Aquarium image.


Species from around the globe are sold for use in aquaria and can become problematic when contents are dumped into a waterbody.

Sail boat in water image.


Aquatic plants and animals can attach to the undersides of boats, motors, and propellers, or in the sea chests and ballast water.

Large pill and various food items.

Food and Medicinals

A number of invasive species may be grown and sold, or hitch a ride on food products, such as exotic apple fruit pests.

Tackle box and pole.

Live Bait

The release of bait into water is a practice that can have significant consequences.

Cargo ship image.

Shipping and International Trade

Vessels can be a significant pathway for the introduction or spread of invasive species through the discharge of ballast water.

Map and compass image.


Travelers may unintentionally carry invasive species, whether they are traveling by air or by land.

Warehouse with stacked boxes.

Biological Supply House

Supply houses provide classrooms with specimens for hands-on, science education. They can introduce a variety of species, such as invasive crayfish, or variable-leaf milfoil.

Firewood image.


Many different invasive pests and diseases can be harbored in firewood, inflicting significant damage to Washington's trees and forests.

Person carrying tulips.

Garden Ornamental

Many species prized for gardens also may be successful invaders, such as English ivy or butterfly bush.

Cattle eating feed.

Livestock and Contaminated Feed

Invasive species can be transported on livestock and in fodder or seed.

Trail in a meadow.

Trail Use

Those who explore nature by foot - on or off trail - may transport unintentionally invasive species on clothing and shoes.

Vehicles in traffic.


Invasive species may be transported on tires, wheel wells, undercarriage, or otherwise on vehicles, farm equipment, and mobile machinery.

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