These invasive mussels were introduced into the United States in 1988 in Lake St. Clair near Detroit, Michigan. The mussels are believed to have been released into the Great Lakes Region from the emptying of ballast water from a Eurasian vessel. So although they have been in the United States for 20 years, the zebra and quagga mussels are new to California. The quagga mussel was first discovered in Lake Mead in January 2007, and quickly spread downstream into Lake Havasu, Lake Mohave, and then into Southern California via the aqueduct system. The zebra mussel was first discovered in San Justo Reservoir, San Benito County in January 2008. Since so many boaters come to Lake County from southern California, the Lake County Board of Supervisors approved an ordinance to protect the water bodies of Lake County from this significant and imminent threat posed by invasive quagga and zebra mussel infestation that can be spread inadvertently through recreational boating.
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