SHIPS - Fish Kill

Map of Lake Washington Fish Kill

Dead fish were found while airguns were being used in Lake Washington. The survey ship never went south of the Highway 520 bridge. Even so, some dead fish were sighted in a southern group near Mercer Island. Significantly, this sighting occured 1/2 hour before the airguns were first used north of Sand Point.

fish observations

The wind blew from the south-southwest all day, so there was insufficient time for dead fish from Sand Point to have drifted 6 miles upwind to Mercer Island. It is clear that something other than airguns killed the fish in this southern group.

Dead fish were also found north of the 520 bridge, along the southern part of the ship track. These fish were observed ahead of and upwind of the ship. Biologists working on the ship's foredeck said the fish were bloated and stinking and had been dead for a long time. The reason why fish in this northern group died is unknown because no fish were recovered.

The survey party immediately instituted procedures to mitigate harm to fish. At our request an investigation of the fish deaths was conducted The preliminary results of the investigation are inconclusive. During the survey we repeatedly sent a small boat to inspect our wake but found no dead fish. Frequently, small boats came from shore to inspect our wake but never reported dead fish.

This fish kill was the subject for front page headlines and much media attention. Several hundred dead fish were first reported; later reports exaggerated this to a miles-long slick of dead fish and finally to millions of dead fish. However, after firing the airguns along the track line shown in red in the figure above, we recovered the airgun array and retraced much of our path to the north, toward Kenmore, where we had earlier discharged the airguns. Thirteen news reporters and six biologists had heard reports of dead fish, and despite their heightened awareness, they sighted no dead fish along our retraced path toward Kenmore. This is the area where the "miles long slick" of dead fish was supposed to have been discovered.

Intensive media coverage continued until it became clear that the fish kill could not be attributed to airgun operations.

Fish Kill Investigation by USGS and State Agency Biologists Remains Inconclusive
--> USGS News Release, March 12, 1998

U.S. Department of the Interior
U.S. Geological Survey
Biological Resources Division
Western Fisheries Research Center
6505 NE 65th Street
Seattle, WA 98115

Contact Dr. Frank Shipley(USGS) Phone: (206) 526-6282 Fax (206) 526-6654

Seattle- Yesterday, a team of specialists from the USGS Biological Resources Division and Washington Departments of Ecology and Fish and Wildlife were unable to observe or collect any dead fish in Lake Washington. The day prior, distressed and dead fish had been reportreed as a USGS seismic survey was undertaken in the lake. Gulls in the area were observed preying on the fish. Dead fish, if they could have been collected, would have been examined and tested for possible causes of mortality.

As part of the investigation, available witnesses were contacted. Accounts indicated fish in distress were first observed at approximately 11:30 a.m. on March 10, 1998, and subsequent observations were reported until about 3:00 p.m. Scientists aboard the University of Washington's research vessel Thomas Thompson began conducting the seismic tests about 11:24 a.m. The ship was stationary off the 520 bridge at the time when fish in distress were first observed. The reported observations suggest the incident may have involved primarily a single species, the peamouth chub. Verification of the species awaits more detailed examination of the single specimen obtained the day of the seismic tests in the Lake.

The witnesses reported a total of 200-300 dead and dying fish in two areas approximately 3.5 miles apart; one site was between Mercer Island and Medina on the east side of the lake, and the other near the Northeast corner of the 520 floating bridge. According to the witnesses, most fish appeared bloated, or were floating on the surface. Some were alive, attempting to dive to deeper water, but could not do so, becoming exhausted and suggesting their air bladders
may have been distended (as would occur if they ascended too quickly from deep water). Unexplained was how the fish observed south of the 520 bridge could have been affected by survey work north of the bridge, given the prevailing southwest wind during the operations.

The investigation team considered a variety of factors that might affect fish including disease and environmental conditions. Dr. Jed Varney, fish pathologist with the Washington Department of Fish and Wildlife reported that "the dissolved oxygen level in Lake Washington was about 10 parts per million, a reading that is essentially normal for the lake at this time of year." The team also collected algae samples. Additional findings are expected following completion of pathology tests on the single dead chub recovered on the day of the seismic tests. According to Dr. Frank Shipley, director of the USGS Western Fisheries Research Center, a record of lake temperatures indicated no abnormalities that might indicate the lake was "turning over," a natural seasonal event that might stress fish. Department of Ecology investigator Dr. Shiela Hosner reported no evidence that a pollution event was involved. "We collected water samples as part of the investigation, and are still awaiting results," she noted "but the field observations were consistent with normal water quality. We checked reference maps for sources of wastewater in the area, but it's a residential area without major sources of wastewater. Discharges or a spill apparently are not a factor."

The seismic survey has now moved to Puget Sound with enhanced monitoring efforts to determine possible effects on fish. An observation boat deployed behind the Thomas Thompson, during firing of the array of underwater compressed air guns every 40 seconds, has reported no dead fish in the wake of the tests.