According to the regional government, the Amhara Highlands receive 80% of the total rainfall of Ethiopia and is the most fertile and hospitable region of Ethiopia. The Amhara Region is the location of Lake Tana, the source of the Blue Nile, at Bahir Dar. The flow of the Blue Nile reaches maximum volume in the rainy season (from June to September) when it supplies about two-thirds of the water of the Nile proper. The Blue Nile, along with the Atbara River to the north, which also flows out of the Ethiopian Highlands, caused the annual Nile floods that contributed to the fertility of the Nile Valley. This supported the rise of ancient Egyptian civilization and Egyptian mythology. With the completion in 1970 of the Aswan High Dam in Egypt, the Nile floods ended. Lake Tana has a number of islands, whose numbers vary depending on the level of the lake; it has fallen about in the last 400 years. According to Manoel de Almeida (a Portuguese missionary in the early 17th century), there were 21 islands, seven to eight of which had monasteries on them "formerly large, but now much diminished." When James Bruce visited the area in the later 18th century, he noted that the locals counted 45 inhabited islands, but wrote he believed that "the number may be about eleven." A mid-twentieth century account identified 37 islands, of which 19 were said to have or have had monasteries or churches on them.