At first this appears to be just a small park with a boat launch, but explorers and fishers can find primitive trails to follow both upriver and downriver.
The paved paths include an approach to the river that is a good place to watch
During high water season, the trails are flooded, but when the river level is low you can explore upriver along the shore, or a primitive trail which then loops back to connect to the field north of the park. I have not fully explored the trail downriver, but it appears to connect to a peninsula on the river which extends over half a mile downriver. Be prepared to climb over logs or other obstacles and pass through brambles with thorns.
Trail at Haapa Park and Boat Launch 
North Fork Lewis River at Haapa Park and Boat Launch 
North Fork Lewis River at Haapa Park and Boat Launch 
North Fork Lewis River at Haapa Park and Boat Launch
I was out at Haapa in December 2021 and found some trees being taken down by a beaver.
This park seems to be targeted toward people planning to spend the day on the river. The facilities there include a restroom (with running water) and a number of picnic tables along the edges.