Olympia oysters (Ostrea lurida) traditionally played important ecological, economic, and cultural roles as the only oyster native to the west coast of North America. Yet overfishing, pollution, and the cultivation of nonnative oysters have driven many historic beds toward or into extinction. Restoration efforts have increased recently in an attempt to reestablish this important ecosystem engineer. In 2012, the Swinomish Indian Tribal Community began a small-scale Olympia oyster enhancement effort in two tidal lagoons with the intention of eventually establishing self-sustaining populations. To properly time future expansion efforts with peak reproductive activity, brooding status was quantified from oyster populations within both lagoons throughout the spring and summer of 2015. Brooding data were compared with water temperature and salinity. Results from this study clearly indicate that northern Puget Sound oysters located in tidal lagoons are capable of brooding at 10.5°C, two degrees colder than has been reported in the literature. Oysters in one lagoon brooded for almost an entire month before the known critical daily minimum water temperature threshold of 12.5°C was reached. These results suggest possible local adaptation or habitat-specific reproductive maturation, and are relevant for Olympia oyster restoration and expansion efforts.