Didn't they used to call those Aqueducts?
" JimH" jimh_osudad@yahooDOT comREMOVETHIS wrote in message
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A water bridge for boats built over a river. Pretty amazing!

http://www.funonthenet.in/content/view/223/31/

http://www.dw-world.de/dw/article/0,,990878,00.html