The Snohomish Estuary is a tidal estuary at the mouth of the Snohomish River. It is approximately 20 sq. miles of islands, sloughs and river channels. Some of the shoreline is industrial, but much of it is natural or being reclaimed. Good birdwatching and wildlife and perhaps 40 miles of sloughs and river channels to paddle.
While this is flat water paddling, the entire area is subject to tides... check the tide tables (see Resources below). One can get substantial tidal currents flowing either up or down river. There also are extensive mudflats in the interior that can be paddled at medium to high tides - a falling tide might strand you for several hours if you are caught unaware.
The area lies within sight of and just east of I5 in Everett. See the Snohomish county park website for an excellent map showing several good launch possibilities.
Tide chart - http://www.dairiki.org/tides/daily.php/ert
Snohomish County Parks & Rec. website:
River/Creek (Up to Class II)