The above video of the San Joaquin River just west of Highway 99 shows a beautiful, living waterway — but beneath the surface, new challenges are emerging.

Water agencies across the San Joaquin Valley have recently detected environmental DNA from invasive golden mussels in canals connected to the Delta and Central Valley water system. These tiny mussels may be small, but their impacts are anything but. Once established, golden mussels can clog pipes and pumps, damage infrastructure, and disrupt native river ecosystems that fish and wildlife depend on.

Because of that Delta presence and ongoing spread via water flow and infrastructure, state agencies are now treating most Central Valley waterways as at risk, but no confirmed established populations have been reported yet near Fresno.

Because our rivers, canals, farms, and communities are all connected, what happens in the Delta doesn’t stay there. Species move — just like water — through the entire system.

Golden mussels (Limnoperna fortunei) are native to large river systems in East and Southeast Asia, including China and parts of the Amur River basin. Scientists widely agree they arrived in California through international shipping, carried in ballast water discharged by ocean-going cargo ships — the same mechanism that introduced zebra mussels, quagga mussels, and other invasive aquatic species.

Once introduced, the Sacramento–San Joaquin Delta provided ideal conditions for the mussels to establish: warm water, steady flows, extensive canals and pumping infrastructure, and few natural predators. From there, they have the potential to spread through connected water systems, boats, water transfers, and high-flow events, putting even inland reservoirs and rivers at risk.

For the San Joaquin River and the Fresno region, golden mussels threaten not just ecosystems, but water delivery systems, infrastructure costs, and the health of native fish and food webs that depend on a functioning river.

Boats are one of the most important ways mussels spread after they become established. Adult mussels can attach to boat hulls, motors, intakes, trailers, and other gear, while their microscopic, free-floating larvae can survive in residual water left in bilges, livewells, ballast tanks, and damp equipment. That ability to move invisibly with water is exactly why “Clean, Drain, Dry” rules exist — they are specifically designed to stop organisms like golden mussels from hitchhiking between waterways.

💧 The Fresno Aquarium project is dedicated to helping the public understand what’s happening right now in our local river, not just what lived here long ago. From invasive species like golden mussels to changing water flows, fish recovery, and river health, our mission is to provide clear, science-based, locally relevant information about the San Joaquin River and the water systems that sustain the Central Valley.