Why is Elevated Total Dissolved Gas (TDG) a Problem?
Saturation of the water with dissolved gases may result from either natural or human caused conditions. High concentrations of TDG negatively impact the health and survival of fish and other aquatic life. The primary source of elevated dissolved gas in the mid-Columbia/Lake Roosevelt is from water spilled at seven dams Priest Rapids, Wanapum, Rock Island, Rocky Reach, Wells, Chief Joseph, and Grand Coulee and from sources in Canada and the United States upstream of Lake Roosevelt. Spill results from river flows exceeding the available capacity of the dam’s powerhouse. Water is also spilled to assist fish passage. The mid-Columbia River’s salmonid populations have declined significantly, and inadequate fish passage has been identified as one of the causes. The habitat the lakes and rivers where fish live also needs to be healthy for the fish populations to recover. This TMDL attempts to balance fish passage needs with the TDG levels necessary to protect habitat. Federal Law Requires Cle
