What is the river called under the Eiffel Tower?

Answer 1

There is NO river 'under' the Eiffel Tower.

However, the Eiffel Tower is in a large garden/park, which borders onto the River Seine.

The River Seine is the river of Paris, France, and flows through the centre of the city, flowing past Les Invalides, and the Notra Dame Cathedral.

The French word. Seine is pronounced as 'Sen'. (Anglice).

Answer 2

There is no river under the tower. But the Seine flows NW of it, about 200 mtrs away, between the tower and the Palais de Chaillot under the Pont D'Iéna.