About the theme

World Rivers runs the big ones — Amazon, Nile, Mississippi, Mekong, Volga, Danube, Yangtze, Ganges, Euphrates, Tigris, Zambezi, Brahmaputra. The long compound river names tile through the grid like the rivers themselves; the short ones (Nile, Indus, Yukon, Congo) are the search hides. The filler reads vowel-heavy because most river names lean on the open vowels of historical geography.