I went to college in Bellingham, and spent a lot of time fishing in three areas. Just depends on how much time you have and fishing style.
First, easy access trout and bass in the lakes around Bellingham - mainly Lake Whatcom and Lake Padden.
Second, the drainage of the North Fork of the Nooksack is next; there are fish year round in the main stem, but I spent most of my time fishing little tributaries in the foothills, upstream of Maple Falls.
Third, and my preference as a backpacker, were the alpine lakes of Mount Baker Wilderness and North Cascades National Park. Obviously, the farther you hike (or the steeper the trail!), the better the fishing. In August all the trails and passes will be clear of snow.
The Skagit is south of Bellingham; I never got the chance to fish it but it is a very special river. As for local contacts, these guys seem to know what they are talking about:
The Confluence Fly Shop.
