Zebra mussels, a prohibited aquatic invasive species, have been found in a variety of moss/algal ball products for aquariums or water gardens sold in western Canada, including in Saskatchewan.
Vermont warns of zebra mussels in home aquarium plant
Invasive Zebra Mussels found in aquarium “moss ball” product in pet, aquarium supply stores - The Rockwall Times
DEC warns aquarium owners of invasive Zebra Mussels found in 'moss balls
UK aquarists warned to be vigilant for invasive hitchhiker - OATA - The Ornamental Aquatic Trade Association
Invasive zebra mussels found in moss ball plants at pet stores
PIJAC UPDATE: Zebra Mussel Problem Growing in Scope - AS Magazine
Pest alert: Invasive zebra mussels arrive in Oregon in moss balls sold for aquariums
Tennessee warns aquarium store owners of invasive zebra mussels
Invasive zebra mussels found hiding in aquarium plants for sale at pet stores - Natural Resources
Pest Alert: Zebra Mussels Found in “Moss” Balls — Oregon Invasive Species Council