Thanks to Jim Borrow for that photo from Upper Alki. He explains:
It’s very difficult to capture this late winter phenomenon with a camera, but the outgoing tide after the 12.0 high at 9:16 a.m has cleaned the local beaches of much of the wood and debris (mostly wood) that has collected over the past year. There likely is an increased amount because of recent river flooding and landslides into the Sound have generated more debris than normal. This band of debris stretched out into Alki side of the mouth of Elliott Bay across our view from Alki Pt. toward Duwamish Head & the city front, gradually dissipating as it drifted to the NE. There have been higher tides, so the wind and wave conditions must have been just right to keep the debris in the water and pull it away from shore. Overall the drift lasted about 1.5-2 hours. Of course this is cyclical and the debris will be redistributed and elsewhere along the shoreline, with a new load deposited on our beaches.
Late last night, Chuck S. sent this photo of what it looked like on Friday along the Beach Drive shore:
Our friends at Beach Drive Blog have posted about this, saying they checked with state and county agencies, who also believe the debris is from recent inland flooding carrying it to Puget Sound.