In the early modern period, the region of southwest Jutland, Denmark, faced international competition and climate change. By the early sixteenth century, the region enjoyed remarkable wealth thanks to a booming fish trade. Catches peaked at levels not surpassed before the twentieth century, and the trade in North Sea herring, haddock, cod, plaice, and skate supported thousands of fishers and merchants. Fishing benefitted from favourable environmental conditions and strong demand from the nearby German market. In the seventeenth century, the region began to decline, primarily because of changes in the international market with competing supplies and declining prices for whitefish relative to agricultural products. Environmental forces had both positive and negative effects on the fishery. The shocks of the Swedish occupation of 1628–29 and the flood of 1634 exacerbated the decline. The demise of North Sea fishing coincided with a shift in urban wealth from middle-class fish merchants to a small group of cattle-trading patricians and led to a general contraction and emigration of the human population along the North Sea coast. The study shows that economic factors and environmental forces must be considered to get a full picture of the region as it faces international competition and climate change.