For four centuries, dykes held back the largest tides in the world, in the Bay of Fundy region of New Brunswick and Nova Scotia. These dykes turned salt marsh into arable land and made farming possible, but by the 1940s they had fallen into disrepair. Against the Tides is the never-before-told story of the Maritime Marshland Rehabilitation Administration (MMRA), a federal agency created in 1948 to reshape the landscape. Although agency engineers often borrowed from long-standing dykeland practices, they were so convinced of their own expertise that they sometimes disregarded local conditions, marginalizing farmers in the process. The engineers’ hubris resulted in tidal dams that compromised some of the region’s rivers, leaving behind environmental damage. This book is a vivid, richly detailed account of a distinctive landscape and its occupants, revealing the push–pull of local and expert knowledge and the role of the state in the postwar era.