With no explanation, label text_A→text_B with either "DON'T KNOW", "NO" or "YES".
text_A: Since the early 20th, when Swan Falls Dam was constructed on the middle Snake River upstream of Hells Canyon, the fifteen dams and reservoirs on the river have posed an increasing problem for migrating salmon. Agricultural lands and their resulting runoff have also had a significant impact on the success rate of migrating fish. Salmon can travel up the Snake River as far as Hells Canyon Dam, using the fish passage facilities of the four lower Snake River dams, leaving the Clearwater, Grande Ronde and Salmon river to sustain spawning salmon. Rising in several forks in the Clearwater Mountains of central Idaho, the Clearwater and Salmon River watersheds are nearly undeveloped with the enormous exception of Dworshak Dam on the North Fork Clearwater River. The watershed of the Grande Ronde in northeastern Oregon, on the other hand, has been fully developed in the latter half of the twentieth century, serving as a reservoir for agricultural and residential use. The four reservoirs formed by the lower Snake River dams—Lake Sacagawea, Lake Herbert G. West, Lake Bryan, and Lower Granite Lake—have also formed problems, as the downstream current in the pools is often not enough for the fish to sense, confusing their migration routes.
text_B: If we assume that the Clearwater River, Salmon River, Grande Ronde, and the North Fork Clearwater River together form a representative sample of watersheds in the northwestern portion of the United States, could this passage lead the reader to believe that half (or more) of rivers in the area are dammed or otherwise put to industrial use?
YES.