A particularly worrisome mussel species has entered North America for the first time through the Sacramento-San Joaquin River Delta — sparking what many are calling an immediate threat to California’s most significant watersheds.

Golden mussels, invasive freshwater bivalves that have devastated ecosystems and critical water infrastructure in other parts of the world, were recently discovered near the Port of Stockton. Limnoperna fortunei appear to have also found their way many miles downstream into O’Neill Forebay of the San Luis Reservoir, where officials in Merced County have been rapidly conducting genetic testing.