In Southern California, as climate and anthropogenic changes continue to alter coastal systems, fish die-offs are seemingly becoming a more regular occurrence in lagoons. These are likely caused by urbanization, but also by restoration efforts that can have undesired effects on several local biotas. Understanding how these different factors impact coastal lagoons and promote fish die-offs is relevant to inform conservation practices. In August of 2018, Malibu Lagoon, which went through two phases of restoration (1983 and 2013), had a massive die-off event of striped mullet, Mugil cephalus. However, the exact environmental process that induced this event is unknown. Hypoxia is the most likely cause of the die-off based on the geologic and atmospheric evidence. The die-off occurred during a heatwave, leaving the lagoon at an average of 27° C, this led to a decrease of dissolved oxygen in the water. At the same time, there was an increase in cloud coverage, decreasing the production of dissolved oxygen by fauna. The low dissolved oxygen level as well as the high abundance of fish and high temperatures would have caused an extensive amount of stress on the fish, quickly leading to their demise. Although, this event could have had multiple other stressors. To further our understanding, we will be analyzing Environmental DNA samples from before, during, and after the die-off. These sediment and water samples will be tested fo the presence or absence of toxic algae, disease, or other species that could be related to the die-off. As well as bacteria present for specific biochemical cycling during the die-off. Conclusions from this study will convey how the geologic processes of lagoons have and will be altered, as well as how these alterations have impacted the species within them.