As the need for data concerning the health of the world's oceans increases, it becomes necessary to develop large, networked communication systems underwater. This research involves the development of an embedded operating system that is suited for optically-linked underwater wireless sensor networks (WSNs). Optical WSNs are unique in that large sums of data may be received relatively infrequently, and so an operating system for each node must be very responsive. Additionally, the volatile nature of the underwater environment means that the operating system must be accurate, while still maintaining a low profile on a relatively small microprocessor core. The first part of this research concerns the actual implementation of the operating system's task scheduler and additional libraries to maintain synchronization, and the second part involves testing the operating system for responsiveness to interrupts and overall performance.