We were on a tour through Ethiopia soon after the summer rains, and much of the country we saw was covered in a green pointillist haze for the time being. We were in Bahar Dar, a substantial town on the edge of Lake Tana, the source of the Blue Nile. A normally wide and shallow outflow within walking distance of our lakeside hotel allowed us a view of the waters at the start of their long journey through Ethiopian gorges until debouching onto the lower lands of Sudan, at Khartoum, where our Nile joins the White Nile, already well travelled from Lake Victoria. From there the combined waters would irrigate an intermittent strip of habitation until reaching Egypt where the population crowded around the river as far as the Mediterranean. Read more . .