Sunken Observation Platform in the Middle of a Pond

There is a clever observation platform built into a pond in  Vöcklabruck, Austria. The platform, rather than being raised, is sunken into the water allowing visitors to walk below the water's surface without getting wet. Pictures of this pond, first reported by Bored Panda, and quickly picked up by other publications, are currently circling the Internet but no additional information seems to have been collected. Some readers speculate what would happen during floods, but if you notice carefully, water is already spilling over the walls into the deck. So there is likely a drainage system in place that keeps the deck water free even during floods or heavy rainfall.
Does anyone know more about this structure and its purpose?
There is similar sunken bridge in the Netherlands.


Photos credit

Credits: Amusing Planet