The lake was a simple flip sim with a boundary that resized and followed the boat. 

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The waterfall was largely a flip sim (with a boundary layer of "air" particles to mimic air mixing in with the water as it falls) that was rendered as whitewater (volumes) where vorticity was high. A layer of mist along the waterfall as well  as at its base where the waterfall met the lake were simmed separately. 

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Finally a few layers of mist were instanced in the background, and the front layer of mist where the boat passed through was simulated with the boat and character as collision objects.

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This piece took three weeks from start to comp. Layout and camera was done in Maya, simulations were done in Houdini and comp was done in Nuke. Redshift was used as the renderer.