The waterfall was going uphill!
Resultant force is the combination of opposing forces on an object. In this case, you have the weight pulling downwards on the water due to gravity and the wind pushing upwards. Normally, the weight is far stronger than the wind. Not only does the water go downwards, but as there is a resultant force, it accelerates downwards. I was unfortunate that the wind was so strong that it was stronger than gravity. The resultant force was upwards and the water accelerated at me.
