Wappa Dam is on the South Maroochy River, upstream from Yandina. The dam is un-gated, meaning it simply overflows through the spillway once it reaches capacity.
The day use area is called Jack Harrison Park, with BBQ and picnic facilities, and toilets with disabled access. There are a few spots to choose from, whether you want to be close to the small playground or nearer to the water’s edge.
The dam itself is not accessible, water activities are not permitted, including swimming, watercraft of any kind, or fishing.
The dam was completed in 1963, one of several dams supplying water to the Sunshine Coast area. At full capacity, it holds 4,694ML (nearly 4.7 billion litres).
Like many dams, the dam wall is fenced off and can’t be accessed. From the fence, there isn’t much that can be seen of the dam wall.
Head behind where the toilet block is, a view of the wall from the front can be seen. There wasn’t much water flowing, barely enough to run down the face of the wall. You can see, however, where the water flows down the wall and into the sides of the rock below at various heights, a decent flow of water will create a wonderful spectacle.
Wappa Falls 
is downstream from the dam, where you can swim. I wasn’t aware of it on the day but I found mentions of being able to walk from the day use area to Wappa Falls, including in the SEQ Water brochure for Wappa Dam. The falls are about 400m downstream from the dam wall, and less than 200m in a direct line from the day use area, so it wouldn’t be too far a walk. If not, take the time to stop by because it is a beautiful spot to have a look at too.