There is a tendency to think of the impacts of hydropower facilities on salmon stocks as a more recent phenomenon, as an issue that emerged in the mid-twentieth century in the period when most of the large-scale onstream dams were constructed in the United States and elsewhere. As evidenced by the quote here relating to the passage of the 1807 River Tweed Act by the British Parliament, however, the law has struggled to reconcile the interests of salmon and hydropower for more than two centuries.2

The River Tweed forms the eastern border between England and Scotland and is one of the most productive salmon and sea trout fisheries in the United Kingdom. As its name suggests, it is associated with the woolen textile mills that began to operate along the waterway in the late 1700s and the early 1800s, mills that were powered by waterwheels. The textile mills along the River Tweed were often built upland away from the river’s edge, and water was diverted to the off-stream waterwheels adjacent to the mills through instream construction of impoundments called “caulds” to collect water, which was then diverted through channels to the waterwheels and then returned downstream back to the river.