There is a need to monitor environmental changes in situ across aquatic ecosystems. Sclerochronology, a systematic biogeochemical method that assesses variations in the accretionary hard tissues of invertebrates, can be useful in studying these changes. Further studies are needed to evaluate whether an equilibrium relationship exists between seasonal annual temperature variations in bivalve shells of species with multiple geographic ranges. We present one of the first sclerochronology reports to characterize the δ¹⁸O and δ¹³C shell profiles of the Olympia oyster, Ostrea lurida Carpenter, 1864. We evaluated its utility as a proxy for past water temperature relating to seasonal cycles. The objectives were to: (1) assess shell δ¹⁸O and δ¹³C values from specimens sampled over time; and (2) evaluate whether δ¹⁸O shell profiles correlate with seasonal temperature patterns. Seven O. lurida specimens were collected, and measurements were taken across shell growth. Results from generalized linear mixed models (GLMM) showed that O. lurida produced δ¹⁸O profiles consistent with a sinusoidal time pattern. The δ¹⁸O values ranged from –2.74‰ to –1.05‰, and there was a significant third-order polynomial temporal relationship. Covariation between profiles of shell δ¹⁸O and δ¹³C values was observed over time. Two independently estimated measures of δ¹⁸O_water, accounting for salinity, temperature, and shell carbonate, were also positively correlated over time. Implications support the theory that O. lurida shell δ¹⁸O profiles may be in isotopic equilibrium with ambient water conditions with applications for monitoring programs.