OK, it is not hard to find--Right out of WDFW
Related to the treaty between US and Canada.

The major effects of the Treaty on recreational anglers in Washington State are Canadian interceptions of chinook and the need to limit our interceptions of Upper Fraser River/Thompson River coho. Canadian interceptions of Puget Sound chinook have decreased since the 1999 renewal, but for certain stocks of chinook salmon, the majority of the harvest is occurring in Canada, and sometimes Canadian interceptions alone exceed the conservation limits for Washington stocks.