A great deal of attention has focused on the basic question of whether higher flows increase salmon survival during the spring management season. The NMFS has conducted extensive research during the spring migration season to get a better understanding of the present level of juvenile fish survival as they pass through the mainstem dams. The results of this research indicate that management measures have increased juvenile salmon survival through selected mainstem projects. This comes as no surprise, however, due to the many factors operating at one time to affect salmon survivals. The value of spring flows is well accepted by the fisheries management community and is supported by a large body of scientific evidence.
Juvenile fish benefit from migration conditions which more closely approximate natural conditions.
This benefit applies to both the river and the estuary environments. For instance, there is a strong body of evidence that increased flow reduces fish migration time. This reduces their exposure to predation, disease, and other factors that may affect their survival in the artificial environment created by the mainstem reservoirs. Increased spring flows also bring us closer to the conditions under which the Columbia River ecosystem evolved, including a large spring freshet, annual flushing and nutritional replenishment of the estuary, and a turbid and nutrient rich plume extending into the ocean. All of these factors facilitate the freshwater to seawater transition.