Get to Whidbey Island and go north. The lake is just north of Deception Pass, right next to the highway on Fidalgo Island. There's a campground right across the road from the parking lot (Cornet Bay?). The campground might be full during prime camping weekends.
It might be just as easy (and you won't have to take a ferry) to go north on I-5 to Burlington, turn left on highway 20 and follow it west and south toward Whidbey Island. You'll go right by Pass Lake adjacent to the highway a mile or so before you get to the Deception Pass bridge. Deception Pass State Park occupies both the north and south sides of Deception Pass and while camping is available it's a very popular place.
From your other post, it sounds like this might be your first lake fishing experience. Just a word of warning, Pass lake can be a real tough lake to fish, while there are big fish in this lake, they don't come easy.
There is camping across the bridge also, about 3 miles away. It also has a lake "Cranberry"
There are fish there brown trout included. But Pass lake is the better of the two. I was up ther 2 weeks ago, and had a lot of luck just trolling a Black leech. I did so s chronimid fishing on
"weed patch". and did really well too. Now if you look at the lake, where the lake bends to the left, At that bend is where the the "weed patch" is. It is very shallow and there are a lot of fish feeding. The key is to be patient and keep your Fly moving (Slowly). Last year there was a bad algea bloom.
And it was hard to fish. When I was there the the water looked very murky. So you might want to hurry. Let me know how you do