Couple of relevant points: - On the new locks they recycle ~60% of the water used already, it's a smart system. - Another commenter pointed out that they have

Couple of relevant points: - On the new locks they recycle ~60% of the water used already, it's a smart system. - Another commenter pointed out that they have to allow fresh water through the lock system to prevent salt water contamination of the lakes. I guess a reason they haven't retro-fitted (yet) the 60% water saving mechanism to the older locks is the scale of the engineering efford involved, plus they can charge people $4.5 million to jump the queue ;)