The construction of the 'Upper Horizons' system commenced in 1968, while the digging of the Fatnicko Polje - Bileca accumulation tunnel began in 1986. Due to the troubles during the 1990's, the construction of the tunnel stopped in 1991, by when some 8 km of the tunnel was completed.

In October 2001, the consortium led by EFT group won the tender to dig the remaining 7 km of the tunnel, complete its internal structure, installations and the entrance control system and accompanying technology. EFT Group invested 23 million euros in these works and the required technology.

The total length of the tunnel is 15.6 km, while its opening is 7.1 meters, which makes it the biggest tunnel so far in south-eastern Europe. The digging of the Fatnicko Polje- Bileca accumulation tunnel was completed with the latest laser-guided technology and was overseen by local experts in Bosnia and Herzegovina.