"Fishing in the river" or "Fishing on the river"?

[Carvalho]

Do we say: Fishing in the river or Fishing on the river?

Thank you

[Cerberus™]

You could be fishing in the river (you drop your angle so that it is in the river), while you are fishing on the river (you are busing fishing sitting in your boat on the river).

[Carvalho]

Thanks for your help!