Looks canalised or big drain with a concrete like walling, The before and after would tell a lot such as flow direction and what to class this as more precisely.
that is not a big drain, compare the waterway to the grass next to it, grass flipped sideways is wider than the waterway.
From my point of view it looks like a ditch or drain (Key:waterway - OpenStreetMap Wiki).
Just post a bigger picture, not this hazy stuff. The drain could be 2-3 meters deep, we have them here, displacing large amounts of water during storm rain or when reservoirs need refilling.
Agreed, but it could as well be a small irrigation channel oder a millstream (feeding a water mill) so from that pic no way to determine what it really is imho.
the drain is like 10-20 centimeters deep
I work on the theory that if a “small” channel is lined with concrete, rock or similar, it’s a drain; while if it’s bare dirt, it’s a ditch.
As they get bigger, they would then become a canal or a stream / river.
According to the wiki the criterion to distinguish between a ditch/drain and a canal is not the size of the waterway but the use. Ditch as well as drain carry superflous or discharge water whereas a canal is made for useful water (irrigation, waterpower, shipping), independent of its size.
I would tag it with