Golden Mussels Found at San Jose Plants
- Valley Water found invasive golden mussels at San Jose’s Penitencia and Santa Teresa treatment plants, the first confirmed detections inside Santa Clara County’s drinking-water system. - One juvenile turned up at Penitencia in April and an adult appeared weeks later at Santa Teresa, showing the species already reached both facilities. - The bigger risk is infrastructure — clogging pipes, filters, and recharge operations as the Delta invasion keeps spreading south.
Golden mussels are tiny, but they can turn a water system into a maintenance nightmare. That is why the discovery at two San Jose drinking-water treatment plants matters so much. Valley Water says the mussels showed up in raw-water areas at the Penitencia and Santa Teresa plants, not in finished drinking water, and the water remains safe to drink. But the news is still a big escalation for Santa Clara County, because it means the invasion has now reached local treatment infrastructure. ### What exactly was found? A juvenile golden mussel was discovered last month in the raw-water intake area at the Penitencia Water Treatment Plant near Alum Rock Park. Then, in late April, an adult golden mussel was found in a raw-water strainer at the Santa Teresa Water Treatment Plant in Almaden. Those are the first known detections tied to Santa Clara County’s local drinking-water treatment system. ### Why are officials saying the water is still safe? (europesays.com) Because the mussels were found before treated water left the plants. Valley Water’s treatment plants disinfect and clean imported and local source water before it goes to retailers, and the agency says its drinking water still meets regulatory standards. So this is not a contamination story in the usual sense. It is an infrastructure story — the kind where the danger is what the organism does to pipes, pumps, screens, and filters over time. ### Why are golden mussels such a headache? They attach to hard surfaces and multiply fast. Once established, they can form dense layers that clog small-diameter pipelines, screens, valves, water intakes, and other equipment. The nasty part is that they also spread in ways that are hard to police — on boats, gear, plants, and in microscopic larval form inside bilges, live wells, and bait buckets. Basically, you do not need to move a visible colony to start a new one. (valleywater.org) ### Why is this species worse than the usual mussel scare? Golden mussels can tolerate brackish water and lower calcium levels better than zebra and quagga mussels. That gives them a wider map. California water managers have been worried about them since October 2024, when they were first discovered in North America at the Port of Stockton and at O’Neill Forebay. Since then, detections have spread through Delta-connected water bodies and major conveyance infrastructure. (valleywater.org) ### How did they get this far south? The short answer is hydrologic connection. Santa Clara County imports a lot of water through systems linked to the Sacramento-San Joaquin Delta, and Valley Water had already warned in April that golden mussels had spread to California water bodies connected to the Delta, including San Luis Reservoir. Once the mussels are in those upstream systems, local treatment plants that handle imported water become exposed even if county reservoirs themselves remain mussel-free. (water.ca.gov) ### What changes now? Expect more filtration, more inspection, and more cost. Valley Water already requires boat inspections at its reservoirs, a program it runs with Santa Clara County Parks, and state water managers have tightened inspection and dry-out rules at infested or high-risk reservoirs. At the plant level, the likely response is more screening, more cleaning, and eventually some redesign of equipment that was never built for a biofouling pest like this. (valleywater.org) ### Why does groundwater recharge come into this? Because Santa Clara County’s water system is not just treatment plants and pipes. Valley Water also manages recharge ponds and other facilities that move water into the groundwater basin. If mussels colonize infrastructure tied to those operations, they can choke off flow and make routine water management more expensive and less flexible. That is the catch — a mussel problem at one intake can ripple into the rest of the regional system. (valleywater.org) ### Bottom line The immediate message is reassuring — San Jose’s drinking water is safe. The longer-term message is rougher. Golden mussels have now crossed from a statewide warning into a local infrastructure problem, and once these things get established, the bill usually arrives in maintenance crews, retrofits, and years of trying to keep pipes clear. (europesays.com) (valleywater.org)
