tdg supersaturation, of course, is not just a Lake Roosevelt issue. The water quality standard for TDG is not being met below dams along the length of the Columbia and Snake rivers. This is why these rivers were put on the list of impaired water bodies (also called the 303(d) list), and a total dissolved gas TMDL is being developed for each.

The Washington Department of Ecology is taking the lead on developing the TMDL for state waters from Grand Coulee Dam down to the Snake River and the EPA is taking the lead, working closely with the Colville Confederated Tribe and the Spokane Tribe, on Lake Roosevelt and Tribal waters below Grand Coulee Dam.

The TMDL will allocate how much TDG can be present above and below each project and still meet the water quality standards. Visit the EPA TDG site for details.