It’s called the upside down waterfall, and it’s not an optical illusion. This amazing phenomenon is explained by the strength of the wind blowing at this place. It is sometimes powerful enough to carry water and bring it back in the opposite direction of the current. The waterfall seems to sink upside down.
Hawaii is not the only place in the world where we find this type of waterfall. This is also the case for the Staubbach and Aegertenbach Falls in Switzerland, Kinder Falls in the United Kingdom, Rjúkandi Falls in Iceland or the Cliffs of Moher in Ireland. Moreover, it is a relatively common phenomenon that can occur in many parts of the world when the force of the wind exceeds the force of the water current, including many places that probably have no name.
Although these natural events are quite common, it is quite rare to see them in real life. They are ephemeral and appear only in certain complex meteorological conditions, involving in particular a period without precipitation followed by a strong flow of wind directed upstream.