Introduction The building of dams in the Pacific Northwest started later in the 19 th century. These early dams were mainly constructed on small rivers or tributaries for the purpose of irrigation. In the first years of the twentieth century, the first hydropower dams were constructed on the tributaries of the Columbia River (National Research Council 231 ). As the century progressed on, dam building activities were stepped up due to the increase in the demand for hydropower. The construction of the Bonneville and the Grand Coulee were initiated in late in the 1930s and this was followed by a marked increase in the number of dams and their storage volumes in Oregon, Washington and Idaho (Bonneville Power Adminstration 3). “Forty five years after the authorization of the Bonneville (1933), 14 dams on the Columbia River and 13 on the Snake River had been constructed” (National Research Council 131). By early 1980s, there were no more sites for large dam construction. Furthermore, public approval for such projects had significantly diminished and thus signaling the end of the growth phase. At the completion of the rapid growth phase it was now obvious that the dams were posing a major threat to ecological sustainability. Most of the “dams were built on the migratory routes of the most west Pacific Northwest salmon runs” (Stewart 45). Various mitigation measures have been taken to address this issue but not much has been achieved. This paper therefore seeks to identify the effects of the Columbia River dams on salmon runs. Though the effects are mostly negative, the paper will go further to identify if there is any benefits that have been created by the dams to the salmon population. Negative effects Many species of salmon breed and grow in the riffles of cold-flowing rivers far from the sea (Stewart 57). The young salmons often migrate to the sea where they live for several years before returning home to breed. The man made dams have prevented the fish from travelling up and down the river ways, despite mitigating measures such as the construction of fish ladders (Dube 13). The insufficiency or lack of fish passage facilities have led to the loss of the upstream habitat. The dams constructed across the Columbia River blocks close to one third of the watershed from being accessed by anadromous fishes. The barriers are mainly associated with the Grand Coulee Dam which accounts for a third of the passage barriers (National Research Council 132 ). The “impassable dams have lead to a significant reduction in the rearing and spawning habitat. However, it is difficult to estimate the magnitude of the loss as record keeping was nonexistent before the dams were constructed” (Pitzer 10). The following are the specific effects of the dams on salmon populations: Dam-linked deaths There dams have been found to account for a considerable number of salmon deaths. Even when the dams are built with fish ladders for upstream passage of salmon, “the fish can still be delayed” (Bonneville Power Adminstration 4, par. 2). The rapid flow of water originating from the turbines usually makes it difficult for the salmon fish to locate the tiny attraction flows that guide them to the ladders. There has been a significant improvement in the ladder design and quality of materials used since the 1900s. However, not much has been achieved in prev