Invasive Mussels Found at SJ Plants
- Valley Water found golden mussels at San Jose’s Penitencia and Santa Teresa treatment plants, the first confirmed detections tied to Santa Clara County’s drinking-water system. - One juvenile turned up in April at Penitencia’s raw-water intake, then an adult appeared weeks later in a Santa Teresa strainer — enough to trigger new controls. - Santa Clara reservoirs are still mussel-free, but the finds show the Delta invasion is now pressing directly against Silicon Valley water infrastructure.
Water plants are built around one basic assumption — the pipes stay open. Golden mussels break that assumption. They’re tiny freshwater shellfish that stick to hard surfaces, multiply fast, and turn intake screens, pumps, and pipes into clogged hardware. That’s why the new detections at two San Jose treatment plants matter even though the water is still safe to drink. Valley Water says a juvenile golden mussel was found in April at the Penitencia Water Treatment Plant and an adult was found later at the Santa Teresa Water Treatment Plant. ### Where exactly were they found? Both detections were in the raw-water side of the system — before treatment, not in finished drinking water. One mussel showed up in the intake area at Penitencia near Alum Rock Park. The other was found in a raw-water strainer at Santa Teresa in the Almaden area. That distinction matters because it means the plants’ treated water wasn’t compromised, but the infrastructure that moves incoming water is now exposed. (mercurynews.com) ### Why are officials worried over just two mussels? Because with invasive mussels, “two” is not the real number that matters. The real problem is whether larvae are already moving through the water system unseen. Golden mussels reproduce quickly, their microscopic young can drift in currents or ride along in wet gear, and once colonies get established they can coat equipment in dense layers. Valley Water has said containment and damage costs can run into the millions if the species takes hold. (mercurynews.com) ### Why are golden mussels worse than the usual mussel story? California already worries about zebra and quagga mussels, but golden mussels are a nastier version of the same headache. They can tolerate a wider range of temperatures and salinity, reproduce rapidly through more of the year, and colonize lots of surfaces. Federal water managers say colonies can exceed 200,000 mussels per square meter. That’s basically biofouling on an industrial scale. (valleywater.org) ### How did they get this close to San Jose? The broader invasion started in the Sacramento-San Joaquin Delta in October 2024 — the first known North American detection. Since then, the mussels have been confirmed in connected water systems, including San Luis Reservoir, which matters for Santa Clara County because imported water moves through those networks. The local plants didn’t get unlucky in isolation. They’re feeling the edge of a statewide spread. (wildlife.ca.gov) ### Are Santa Clara County reservoirs infested now? Not yet. Valley Water says no golden mussels have been detected in any Santa Clara County reservoirs. But that clean status now looks more fragile. The agency has rolled out prevention measures, including mandatory inspections for all watercraft using local reservoirs, and it’s pushing the usual but essential rule: clean, drain, and dry everything that touched the water. ### What changes now? The practical response is pretty unglamorous — more screening, more monitoring, more operating changes, and more money. (wildlife.ca.gov) Valley Water says it now has to install removal equipment at some facilities, tighten boating controls, and limit how some groundwater recharge ponds are used this year. State agencies were already in response mode before this, with California publishing a formal response framework in April 2025 and offering grant money to help boating facilities stop the spread. (valleywater.org) ### Does this mean drinking water is unsafe? No. The water remains safe to drink. The threat is to the machinery and to the long-term cost and reliability of moving water around — not to potability from these detections themselves. That’s the part people often miss. Invasive mussels are less a contamination story than an infrastructure story. ### Bottom line? San Jose’s water didn’t suddenly become dangerous. (mercurynews.com) But Silicon Valley just got a very concrete sign that California’s golden mussel problem is no longer a distant Delta issue. It has reached the front door of local water treatment infrastructure.
