OSM Wiki describes the general approach. Because there is so much variation in the world, it's only an approximate guideline. The goal is to describe the functional purpose of the element. "Jumping across" is a good indication that something might be a river, but that doesn't mean so - it can be a canal, a drain or large ditch or indeed a stream. We have to look at how it compares to other rivers across Latvia. And this example is different than typical due to HES. Here it fails two of the main criteria - it's not a significant flowing body of water and it doesn't actually flow into anything. It doesn't flow into Daugava, it ends at the canal and it doesn't even feed the canal much. Most of the stream is wide exactly because it doesn't flow - the water just accumulates because it has nowhere to go. And it has nowhere to go because nowadays these are all just large melioration ditches that follow some of the original waterways. This is why there are ponds and small lakes here - it's where the water ends up. And we only tagged this as a stream because it's larger here when fed by ditches and not being able to flow anywhere. But that's a long way from a river for what is just a big ditch. It was tagged as a ditch for a decade before another local mapper began changing these.

You can find many examples of several meter wide ditches, like https://www.openstreetmap.org/way/1029646110 , but these aren't rivers unless they actually form the primary ways for a tributary network and serve as the outflow for it.

Bluķupe should not be a river either. It was changed recently and it is a similar mistake. No one just noticed it. That one is even smaller than this one.

As I mentioned, historic local classification is not the same as the current real-world status, so that wouldn't matter. And more importantly other maps don't necessarily match OSM meanings for such things. Soviet maps used to call pretty much any named long natural waterway a river.

Similarly, original flow of the waterway before HES or area development wouldn't really matter. As I mentioned, it is semi-artificial - some of it matches the original layout, but much of it has been "straightened" around areas. And historical streambeds and riverbeds do not determine the current status.

Anyway, those are my thought on this because I have looked at this location before and surveyed the area around. I do not believe it comes anywhere close to a river classification because it is a large ditch that is probably ok to call a stream due to its appearance.