Fish and Aquatic Conservation

Destroy! Don’t Dump!

Invasive zebra mussels have been found in "moss balls,”plant product sold at aquarium and pet supply stores, garden centers, florist shops, and online retailers.  Zebra mussels are regarded as one of the most destructive invasive species in North America.

Zebra mussels can quickly take over once they get established in a waterbody and cause significant damage including disrupting the food chain, changing the chemistry of the water (which can cause more blue green algae outbreaks or offensive taste), and clogging water intake and delivery systems. The concern is that live mussels released into a storm drain or flushed could be introduced into a waterway.

What are “moss balls?”

A moss ball is a species of green algae that is formed into a ball and is 2 to 5 inches in diameter. Moss balls are used in home aquariums, terrariums, and water gardens.

What should I do if I recently purchased moss balls for my aquarium or water garden?

If you purchased a moss ball aquatic plant product after February 1, 2021, we recommend that you take the following steps to destroy and dispose of the moss ball to reduce the risk of any zebra mussels escaping to waterways and causing harm.

Do not dispose of the moss balls in drains, waterways, or gardens. Moss balls must be destroyed and disposed of in a sealed container in the trash.

When following any of the methods listed below, ensure that the disposal method you choose is in compliance with your local state laws and animal welfare regulations.

DESTROY in one of three ways:

  • Freeze - Place the moss ball into a sealable plastic bag and freeze for at least 24 hours.
  • Boil - Place the moss ball in boiling water for at least 1 full minute.
  • Bleach / Vinegar - Submerge the moss ball in regular, unscented bleach, diluted to 1/3 cup per gallon of water, for 10 minutes; or undiluted white vinegar for 20 minutes.

DISPOSE of the moss ball and any of its packaging in a sealed plastic bag in the trash. If vinegar, boiling water, or bleach was used, the liquid can be disposed down a household drain —never down a storm drain where it could enter and damage local waterways.

DRAIN and clean the aquarium. (Updated with additional guidance on 3/18/21)

Collect any fish or other living organisms and place them in another container, with water from a separate, uncontaminated water source. Remove contaminated water from the tank and sterilize by adding 1/3 cup of bleach for each gallon of water. Let the water sit for 10 minutes and then dispose the sterilized water down a household drain.

Clean the aquarium and accessories using ONE of the following methods, ensuring that the decontaminate method you choose is in accordance with manufacturers’ recommendations:

  1. Hot Water Method:
    • Use water that is 120 degrees F to flush and coat the tank and all accessory surfaces for at least two minutes.
  2. Salt Water Method:
    • Make a saline solution using ½ cup of salt per gallon of water and soak aquarium substrate, rocks, décor, and filter media in salt water solution for at least 24 hours.
    • Dispose of the treated water in a household drain and rinse all items prior to setting up the aquarium.
  3. Bleach Disinfection Method:
    • Make a disinfection solution using 1/3 cup of bleach per gallon of water.
    • Soak the aquarium, substrate, rocks, décor, and filter media in the bleach water solution for 10 minutes.
    • Rinse off all items prior to setting up the aquarium.
    • Dispose of the previously used filter media and replace with new media.
    • Use a dechlorinating product to neutralize any residual chlorine prior to reintroducing aquatic life.

What should I do if I have a water garden or am unable to disinfect my aquarium?

Decontamination using the steps above is highly recommended and essential if mussels are observed; however it is understood that many aquarists and water gardeners make significant investments in establishing and maintaining their systems and that discarding all water and reestablishing a system in which mussels have not been observed may not be ideal. As alternatives , and consistent with steps necessary to prevent the release of zebra mussels, aquarists and water gardeners may follow a Potassium Chloride or quarantine method. Please refer to the link below for detailed instructions.

A more detailed list of DESTROY, DISPOSE, DRAIN instructions can be found here. (Updated 4/27/21)

Quick Links
moss ball and zebra mussels
Moss ball and Zebra mussel. Photo by IDFW

A person holds a small mussel in their fingers. Attached to the top are two smaller zebra mussels.
Zebra mussels can quickly take over once they get established in a waterbody and cause significant damage.

What you need to know about aquarium moss balls and zebra mussels

On March 1, 2021, U.S. Geological Survey (USGS) scientists were alerted that zebra mussels were found attached and inside moss balls sold as aquarium plants. Zebra mussels are an invasive species that can devastate local ecosystems and infrastructure. Zebra mussels are currently invasive in several states, and we need the public’s help to ensure this dangerous invasive species does not spread further.

What is an aquarium moss ball?

Aquarium moss balls are not moss but a green filamentous algae (Aegagropila linnaei) that looks like moss. They are soft and spongy when filled with water in aquariums and provide habitat for fish, shrimp, and other species. Moss balls are hearty and easy to maintain and are an active commodity in the aquarium trade. Moss balls can be purchased in every state through national retail chains, small independent retailers, and online marketplaces.

The species is found mainly in areas of Northern Europe and in several places in Japan. It has rarely been found in North America and Australia. The moss ball itself is not found to be invasive.

Where are contaminated moss balls coming from?

Zebra mussels are native to Eastern Europe in the Black, Caspian, and Azov seas. It is unknown whether contamination is occurring within the supply, distribution, or retail chains. Additional assessments will be needed to understand the origins and magnitude of the problem.

What are zebra mussels, and why are they a problem?

Zebra mussels are one of the most devastating invasive species in North America. When they become established in an environment, they alter food webs and change water chemistry, harming native fish, plants, and other aquatic life. They clog pipelines used for water filtration, render beaches unusable, and damage boats. These filter feeders outcompete other native species in infested rivers and lakes. The waste they produce accumulates and degrades the environment, using up oxygen, making the water acidic, and producing toxic byproducts.

Where have zebra mussels on moss balls been found?

As of March 4, 2021, zebra mussels found on moss balls have been reported in Alaska, Arizona, Arkansas, Colorado, California, Florida, Georgia, Idaho, Indiana, Iowa, Louisiana, Maryland, Montana, Nevada, Nebraska, New York, North Dakota, Oklahoma, Oregon, South Dakota, Texas, Virginia, Vermont, Wisconsin, Wyoming, and Washington.

What needs to be done immediately to manage the invasive risks of zebra mussel contaminated moss balls?

Zebra mussel contaminated moss balls must be properly disposed of throughout the supply chain, including retail stores, on-line commerce, and home tanks of aquarists.  

What stores or products were contaminated?

At this time, we do not know the full extent of stores or products containing zebra mussels. If you have recently purchased moss balls from any retailer, we recommend they be destroyed following our Destroy, Dispose, Drain instructions.

What should I do if I recently purchased a moss ball?

Until we know the extent of the moss ball contamination problem in the United States, we are recommending that recently purchased moss balls be destroyed, the water decontaminated, and tanks cleaned according to the instructions on our website.

Can I just quarantine my moss ball for a few months rather than destroy it?

Zebra mussels can damage your tank's filtration system. Zebra mussel larva can live in the water, in the aquarium substrate, on decorative elements, and in the filter systems. Until we know the extent of the moss ball contamination problem in the United States, we are recommending that recently purchased moss balls be destroyed, the water decontaminated, and your tank cleaned according to the instructions on our website.

I found a zebra mussel in my moss balls. Do I need to report it?

Reports of zebra mussels attached to moss balls should be submitted to the USGS Nonindigenous Aquatic Species data base.

Upon submission, the information you provide is sent to USGS staff experts for verification. Follow the Destroy, Dispose, Drain procedures outlined on our website.

For questions or concerns specific to your state, reach out to your local fish and wildlife agency.

What is USFWS doing to fight aquatic invasive species?

The U.S. Fish and Wildlife Service’s Branch of Aquatic Invasive Species funds and coordinates aquatic invasive species activities across the country.  Our regional coordinators work closely with the public and private sector partners, and our Fish and Wildlife Conservation Offices provide research and technical support. The Service also develops regulations to prohibit the importation and some transport of high-risk species known as injurious wildlife.

State news releases, as of March 7, 2021:

If you have any questions regarding zebra mussels and the safe disposal of moss balls, please contact us.