Confluence of the Ilz, Danube, and Inn Rivers in Passau, Germany.

The Ilz is a relatively small mountain stream and has a blue-ish color while the Inn is a fairly large river flowing in from Salzburg, Austria at the top. The Inn River has more water flow than the Danube, yet flowing away from the city the three combined rivers are called Danube.
This photo is taken from the Oberhaus-fortress (now a city museum) on top of the Ilzstadt cliff above the city of Passau in Lower Bavaria, Germany. It is also known as the Dreiflüssestadt or “City of Three Rivers”