Golden mussels found in San Jose water

Drinking water is still safe in San Jose. That is the first thing to know. The news is not about contamination in the usual sense. It is about infrastructure — the machinery that moves and cleans water — and a tiny invasive mussel that is very good at turning pipes, screens, and filters into maintenance problems. Valley Water says golden mussels have now been detected at the Rinconada and Penitencia water treatment plants in San Jose, which makes the threat feel a lot less theoretical. ### What is a golden mussel? A golden mussel is a small freshwater bivalve native to Asia. The reason water agencies hate it is simple — it reproduces fast, sticks to hard surfaces, and forms dense colonies. Those colonies can clog small-diameter pipelines, screens, filters, valves, pumps, and other equipment that water systems depend on every day. ### Why is this a big deal in California? California had not seen golden mussels in North America until October 2024, when state staff found them at the Port of Stockton. (mercurynews.com) That already worried water managers because this species can handle conditions that zebra and quagga mussels often cannot, including brackish water and lower calcium levels. Basically, more of California’s water system is vulnerable than it would be with some other invasive mussels. (water.ca.gov) ### Why do treatment plants care so much? A treatment plant is full of surfaces and choke points. Water passes through intakes, screens, basins, pipes, and filters in a tightly controlled sequence. A mussel infestation does not need to poison the water to cause trouble. It just has to build up in the wrong places and force more cleaning, more shutdowns, more replacement parts, and more protective equipment. Valley Water has already warned that once golden mussels take hold, containment and infrastructure damage can cost millions. (water.ca.gov) ### If they are at the plants, is the tap water unsafe? No — the agency’s message is that the water remains safe to drink. The issue is operational, not a sign that the treated water itself has become hazardous. But “safe” does not mean “no problem.” The catch is that the district now has to harden parts of the system against a pest that is difficult to remove once established. (valleywater.org) ### How do these mussels spread? They hitchhike. Adults can cling to boats, trailers, docks, plants, and gear. Their microscopic larvae can move in bilges, live wells, or even leftover water in bait buckets. That is why water agencies obsess over boat inspections and the “clean, drain, dry” routine — the spread often comes from moving wet equipment from one waterbody to another. (mercurynews.com) ### What does this mean for Santa Clara County now? The immediate irony is that Valley Water has said its reservoirs were still mussel-free even as the regional threat kept rising. Now the district has confirmed detections at two treatment plants, while still trying to stop the species from establishing more broadly in local source waters. That likely means tighter inspections, more monitoring, and changes to how water is moved and processed before the problem gets bigger. (valleywater.org) ### Why are officials so worried about reservoirs? Because once mussels establish in open water, control gets much harder. State water managers already treat several connected State Water Project reservoirs as infested or high-risk, and they use entrance inspections plus dry-out periods for boats to slow the spread. Santa Clara County’s best-case scenario is to keep local reservoirs from joining that list. ### Bottom line? (valleywater.org) This is a water-infrastructure story, not a drinking-water panic story. San Jose’s water is still safe. But golden mussels have moved from distant warning to local operational headache, and once they get into a system, the bill — in money, labor, and constant vigilance — usually only goes up. (mercurynews.com) (water.ca.gov)