This is a stilling basin (also known as an energy dissipator.
Located at the base of a dam, it takes the fast-moving water and forces it into intense turbulence which dissipates most of the water's kinetic energy. This prevents dangerous erosion and scouring of the riverbed.
Peter Lammer is chef in a restaurant in Germany. He was involved in a motorcycle accident and, after rehabilitation, doctors advised him to retire.
Together with his friends, he came up with this effective mobile seat.
Along with reduced risk of injury, the underwater runner experiences longer runs as well.
Aqua jogging on an underwater treadmill also takes advantage of viscosity: water's natural drag strengthens the muscles.
[📹 aquamaxx_gz]