For over a hundred years, stretches of the main stem of the Walla Walla River ran dry in the summer months due to agricultural diversion of the river water. Salmon runs and several native fish populations became threatened and, as a result, were listed under the Endangered Species Act. Because of actions taken by local and state agencies concerned with the health of the river, it no longer runs dry in the summers and the fish populations are improving.
Change in flow is a key determinant of a river's health. Changes in flow are caused by human and natural actions. These include rainfall, snowfall, temperature, and draws for potable, industrial, and agricultural use. Without adequate flows, fish do not have enough water to live, the water becomes too warm to support a healthy fish population, and pollution from municipalities, industries, residential fertilizers, and pesticides is concentrated in a smaller amount of water.
The flow change most critical to a river's health is the level occurring during the lowest flow days of the year. During these periods, biological systems are put under the greatest stress. To ensure the river's health, state agencies are working collaboratively to establish a minimum flow that will protect fish and other aquatic life and preserve human uses such as recreation.
This indicator measures the lowest seven-day average river flow per year of the Walla Walla River. Specifically, the Walla Walla River is measured near Touchet (approximately three river miles upstream from U.S. Hwy. 12).
