Beautiful Spot!!
Camano Island State Park has a beach, camp sites and a hiking trail. They even have little rustic cabins for rent. That would be a fun low key weekend trip. The hiking trail is a little 3 mile loop with beautiful views.
When you enter the park if you keep driving to the end of the road you’ll get to a large parking lot. Drive to the furthest point of that and you’ll reach this beach access. This is a great place to walk on the beach or let your dog go for a swim.
On your way home I recommend stopping at the Camano Island Inn and getting a glass of wine and a snack. They have a big back yard with tables and will allow your dog to dine out there with you if it’s not too crowded. There is a lovely view of the water and you can pick a table on their deck or right on the lovely grass.