A total of 22 green sturgeon (Acipenser medirostris) collected from California and Washington were examined for parasites. This included five freshwater young-of-the-year, five estuarine juveniles, and 12 adults captured in freshwater on their spawning run. None of of the freshwater young-of-the-year were infected. All estuarine juveniles and all spawning adults were infected with at least one kind of parasite. Eight species of parasites were recovered. These included one protozoan (unidentified), two monogeneans (Nitzschia quadritestes, Paradiclybothrium pacificum), Two cestodes (unidentified metacestode, Amphilina sp.), two nematodes (Anidakis simples, Metabronema sp.) and one isopod (Lironeca vulgaris). Nitzschia quadritestes proliferated on two fish held in saltwater aquaria. One estuarine juvenile died as a result of heavy Nitzschia infection. One adult was treated with formalin. A standard one-hour formalin bath at 250 ppm had no visible effect on the parasites. Extending the treatment time to 3.5 hrs caused a decrease in abundance but did not eradicate the parasites. Parasite numbers rebounded within two months. Nitzschia could be a significant problem in salt water rearing of green sturgeon.