Better monitoring of fish in dam projects

Inadequate ecological monitoring before and after removal of dams in the northwestern United States is hampering evaluation of the success of dozens of these projects (see Nature 511, 521–523; 2014).

A primary purpose of dam removal in the region has been to revive populations of endangered migrating salmonid fish by restoring natural river functions. Populations are being monitored after demolition of the 38-metre Condit dam and 64-metre and 33-metre Elwha dams, but these are exceptions.

Using fish ladders, salmonids were able to ascend the Marmot and Hemlock dams you mention and move into the upper river. But to gauge the ecological impact of such dam removals, it is necessary to have baseline data on fish passage from before the structure was destroyed. In most other cases, these data are not available, thwarting future assessments.

Long-term ecological evaluation and monitoring must be built into dam-removal projects. Otherwise, millions of dollars will continue to be spent with no evidence that the desired outcome is being achieved.