Why does the Ganes in the Four Rivers Fountain in Rome hold an oar?

Question

Why does the Ganes in the Four Rivers Fountain in Rome hold an oar?

Answer 1

the Ganges of the fountain holds an oar to show that the river is navigable.

this link is in Italian, but it's where  I found this information:

http://www.romasotterranea.com/index.php...

there are informations about the other 3 rivers:

the Nile has his face covered because the source was unknown

the Danube has a crown of flowers over his head

the Rio de la Plata has a scared face because there's a snake in front of him