Hawaiʻi is home to ʻoʻopu nākea (Awaous stamineus), a culturally significant, endemic, freshwater goby that exhibits an amphidromous life cycle (freshwater to saltwater to freshwater migration), characterized by a marine larval stage followed by post-larval recruitment to streams, where they live to become reproductive adults. However, recently a research group suggested that some individuals complete their entire life cycle in freshwater streams. Despite their importance in Hawaiian traditions and the ecology of Hawaiian freshwater ecosystems, we still lack a full understanding of their migratory patterns and life history due to the difficulties in determining the environmental migratory cues that set the timing and location of their migratory paths. This study aims to examine the amphidromy of ʻoʻopu nākea and whether environmental factors, such as mean annual rainfall, streamflow, and water chemistry influence amphidromous migration. We sampled 90 individuals from three streams on the windward side of the island of Oʻahu: Waimanalo, Kahaluʻu, and Kahana streams, that represent a range of hydrological variability across the state. Amphidromy was tested using elemental analysis (strontium:calcium ratios) of sagittae, the largest pair of otoliths (calcareous ear structures) to examine if individuals spent their larval period in the ocean or if they never left the freshwater streams. We found that 100% of the otoliths that were readable had clear marine levels of strontium, showing an obligate amphidromous life cycle. This study is a key step in understanding the life history of ʻoʻopu nākea, and furthermore highlights the importance of upstream-downstream connectivity for the survival of amphidromous species, that are typical in many tropical islands (e.g., Puerto Rico) and Pacific regions (e.g., Taiwan, Japan, and Australia). This Hawaiian study of ʻoʻopu life histories will contribute to our knowledge of amphidromous fish species to better inform management and conservation practices worldwide.