People often ask about the driftwood on our local beaches. It certainly adds character to the shoreline. I was unable to find any regulations that generally prohibit the collection of such driftwood, although specific prohibitions may exist. For example much of the shoreline on Whidbey Island is considered private property down to the low-tide mark. Yet, on other beaches the private property ends at the high-tide mark so it is difficult to tell if you are on private property or a public shoreline. Many of the public beaches are also part of State Park property and each park may establish some restrictions, while I could not find any general prohibition on collecting from the state park beaches.
In some cases local residents may object for environmental reasons and prefer the driftwood to remain. The driftwood serves as habitat for insects that become part of the food supply for the local salmon. In certain references I found that legality to collect it might just depend on the source of the driftwood; such things as “piling poles” and logs may be restricted. It’s probably best to stick to the smaller pieces that you can easily carry. Here are some sources and references: