Personally I prefer Anakin going over the waterfall but yes the issue of the lightsabre is a stickler. You know, it might be possible to still have a trimmed down version of the river bank scene with Obi-Wan and Anakin after the bridge goes over and perhaps cut around the Yoda fight. But anyway, at least the seed is planted and anyone/everyone can have a play around with the idea.
Cheers.
Dantha.