[kpetermeni]

Libya's Great Man-Made River (1,750mi, 2,820km) [0] would like to have a few more words :-). [0] https://en.m.wikipedia.org/wiki/Great_Man-Made_River

[nottorp]

Let's nitpick then. It says: "According to its website, it is the largest underground network of pipes (2,820 kilometres (1,750 mi))[3] and aqueducts in the world.".

It could concievably have no pipe longer than 114 km.

Also if it's underground it's not a river?

[stickfigure]

https://en.wikipedia.org/wiki/Subterranean_river

[afterburner]

That's a heck of an aquifer. Libya is pumping 2.4 km^3 a year from the estimated 150,000 km^3 reserve.