Conventionally a minimum size is used for picking features to label based on the number of pixels. This works well for most cases (e.g. buildings) because features below a certain size are too small to label and those above that size are significant enough that they need labeling.
This does not work well for water which tends to have long curvy areas like rivers that have lots of pixels but shouldn't be labeled.
The river in this case is >1024 pixels, but labeling it would be absurd.
I think there are three relevant cases
- A mostly straight river aligned with its bounding box
- A mostly straight river not aligned with its bounding box
- A not straight river