Near the city of Manaus (1,000 miles upriver), the dark, almost black, waters of the Rio Negro, flowing south from Venezuela, meet the light coffee coloured waters of the Amazon River. This meeting of the waters goes on for about 3.5 miles (7km) downstream and is due to the differences in temperature, speed and water density of the two rivers. It is a popular tourist attraction. We were able to view it from our cruise ship, as well as on a boat tour the next day.