Aquatic invasive species 

Our local waters provide many opportunities to fish, boat and swim. However, when we travel from one waterbody to another we can accidentally carry along invasive plants and animals. Invasive species grow rapidly and harm native plants and animals and can make recreation difficult. The good news is you can take action to help stop the spread of these harmful plants and animals.

Help stop the spread

Invasive species can be transported and spread by fishing gear, boats, jet skis, trailers, kayaks, waders, and other equipment. Whenever you are leaving a lake, river, or the Puget Sound, help protect other waterbodies and Clean, Drain, and Dry your equipment and boat:


Person picking invasive species off boat and trailer

Check, remove, and throw away mud, plants, and aquatic life (mussels, milfoil, etc). 

Boat draining on boat ramp to remove invasive species

Drain all water from gear, boat, motor, bilge, ballast, wells and any compartments.

Person drying boat to prevent the spread of invasive aquatic species

Dry everything fully before going to a different waterbody (air dry 5 days or towel dry).


Why are invasive species harmful? 

Invasive species are plants or animals that have spread to areas where they don’t naturally occur. They often have no natural controls so they can spread rapidly and displace the native species that are there naturally. This causes changes in the habitat and food chains that can make it harder for native species such as salmon to survive.  

Invasive species also harm recreation. Invasive plants like Eurasian watermilfoil form dense mats that can entangle swimmers, fishing line and boat motors. Invasive animals like New Zealand muds snails grow so dense they can make beaches unusable, destroy motors and clog water intake pipes.


Which aquatic invasive species do we have in Snohomish County?

Eurasian watermilfoil, Brazilian elodea, Parrotfeather, and New Zealand mud snails have been found in a few places in Snohomish County. It is important to stop these species from reaching other nearby lakes and streams.  

Eurasian_watermilfoil_growing_densly Opens in new window
Eurasian watermilfoil
New Zealand mud snails

Which aquatic invasive species are in the region?

Hydrilla, Variable leaf milfoil and Flowering rush are invasive plants that have been found in Washington State but not Snohomish County. Zebra and quagga Mussels are still a couple of states away but are headed this way. Clean, drain and dry your equipment every time to stop these invasives from reaching our area. 

Brazilian elodea
Quagga_mussel_on_blue_backgroundquagga/zebra mussels

Where can I learn more about invasive species?

Snohomish County's Lake Management Program's  native and invasive aquatic plants webpage has resources for you to identify aquatic plants and options to control invasive species.

You can learn more about about all invasive species in rivers, the Puget Sound, and on land from the Washington Invasive Species Council. Find out more about invasive plants and their control from the State Noxious Weed Control Board or the Snohomish County Noxious Weed Control Board

What do I do if I see an invasive species?

If you suspect an invasive species in a Snohomish County lake, send a photo to For other locations, report sightings to the Washington Invasive Species Council.