Mono Lake is a hypersaline soda lake rich in dissolved inorganic arsenic with its primary production currently dominated by <i>Picocystis</i> str. ML. We set out to determine if this picoplankter could metabolize inorganic arsenic, and in doing so form unusual arsenolipids (e.g., methylated arsinoyl ribosides) as reported in other saline ecosystems and by halophilic algae. We cultivated Picocystis str. ML on an inorganic seawater-based medium with either low (37 µM) or high (1,000 µM) phosphate in the presence of arsenite (~0.4 mM), arsenate (~0.8 mM), or without arsenic additions.