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. Dykeland was in danger.rnrnAgainst the Tides is the never-before-told story of the Maritime Marshland Rehabilitation Administration (MMRA), a federal agency created in 1948. As farmers could not afford to maintain the dykes, the MMRA stepped in to reshape the landscape and with it the communities that depended on dykeland. Agency engineers borrowed from some of the farmers’ long-standing practices, but they were so convinced of their own expertise that they sometimes disregarded local conditions, marginalizing farmers in the process. The engineers’ hubris led to construction of tidal dams that compromised a number of rivers, leaving behind environmental challenges.