First lets define upwelling
Upwelling- a rising of seawater, magma, or other liquid
In this case, you would be looking at a river, lake, ocean, or other body of water good for fishing.
You'd want to look for a place with upwelling because when there is a rise of water, the sea creatures within it will rise too. So the fish in the bottom of a lake for example would be brought up to the surface of the water or near the surface which is where your fishing rod is trying to grab the fish.
I hope this helps! Don't be afraid to reach out with any further questions!
