A nuanced history of seafaring communities in the Indian Ocean, where the force of British imperial power depended on the expertise of local divers and sailors to feed a global demand for pearls. In the late nineteenth century, thousands of men and boys across the northern rim of the Indian Ocean dove daily to the ocean floor in search of pearl-bearing oysters. It was the height of the so-called global pearl boom, driven by enormous demand for pearls in Europe and North America. Far removed from the showrooms of New York, London, and Paris, these divers drew on skills and expertise handed down across generations to conduct the dangerous work of hauling oysters up from the warm shallows. But they also faced a new challenge: the rise of British power in the Indian Ocean, where colonial officials relied heavily on local knowledge and labor to feed the lucrative pearling industry. Tamara Fernando examines the transformations wrought by colonial extraction across the three primary sites that fed the pearl boom between 1850 and 1930: the Persian Gulf, the Gulf of Mannar near Sri Lanka, and the Mergui Archipelago in Myanmar. British oversight transformed migration patterns and the dynamics of race and caste among divers, while imperial scientists regularly tested new technologies and techniques intended to improve oyster hauls. Yet even as the positions of local divers and sailors changed dramatically, their expertise remained paramount to the industry—until, in the 1930s, the depletion of oyster beds and the rise of lab-grown alternatives shuttered the market for natural pearls altogether. A vivid account of how seafaring communities navigated these shifting tides, Shallow Blue Empire fundamentally recenters the human labor, animal lives, and environmental conditions that sustained a global obsession with pearls.