I am working on a project that will replace some anchor cables on the
two floating bridges that cross Lake Washington in Seattle, Washington.
The project will use a pair of divers to replace these cables in water
from 40 to 200 feet deep. Lake Washington is the largest lake in
Western Washington, and supports a number of salmonid species, including
anadromous sockeye. Adult sockeye are known to find thermal refuge at
50 to 90 feet deep during the warmest part of the summer, and this
season the population is expected to be 105,000.
A question has arisen on the potential impact that two divers would have
on these fish, and I am at a loss to find a source of information. Does
anyone know, or can anyone provide best professional judgment, on the
potential impact of a pair of divers moving vertically through the
thermal refuge layers where sockeye would be dispersed?
NW Region Biology Program Manager
Washington State Department of Transportation