According to materials published by the Central Statistical Agency, the Blue Nile has a total length of 1,450 kilometres (900 mi), of which 800 kilometres (500 mi) are inside Ethiopia. The Blue Nile flows generally south from Lake Tana and then west across Ethiopia and northwest into Sudan. Within 30 km (19 mi) of its source at Lake Tana, the river enters a canyon about 400 km (250 mi) long. This gorge is a tremendous obstacle for travel and communication from the north half of Ethiopia to the southern half. The canyon was first referred to as the “Grand Canyon” by the British team that accomplished the first descent of the river from Lake Tana to near the end of the canyon in 1968. Subsequent river rafting parties also called this the “Grand Canyon of the Nile”. The power of the Blue Nile may best be appreciated at the Blue Nile Falls, which are 45 metres (148 ft) high, located about 40 kilometres (25 mi) downstream of Lake Tana.