Golden mussels, an invasive species that officials across the country have been worried about for years, invaded North America for the first time through the Port of Stockton.

Before arriving in North America, the species is believed to have invaded South American rivers through ballast water—the fresh or saltwater that is held on ships. In 2021 in Brazil they had invaded about 40 percent of the country’s hydropower plants, according to Science’s Sofia Moutinho in October of that year.

Water officials around Lake Tahoe are on high alert after an invasive species of mussel was found near Stockton and for the first time in North America, according to the Lake Tahoe Environmental Improvement Program.

The tiny freshwater mollusks, which have already laid siege to waterways of southern South America, were found at Rough and Ready Island, near Stockton.