That picture looks like alot of the google sat pictures and the author named the subject, searching for the subject and gdoing a google translation of those pages into english;
Do a search for basin or "methods of irrigation" it discusses a check system, and then describes the basins, and does a good job of describing what we see in those pictures.
So - I say its for sugar beet farming, from french picture titles, other french descriptions on a map, and a 1913 farming manual. So - I would say these basins could very well have been there since WWII.
Elsewhere on the web you can find that sugar beets is basically the sole source of sugar for belgium, and that production has only slowed down slightly. I found a export graph of sugar beets, and Belgium had major spikes of sugar beets in the 60's-70's. Before and after that time, virtually no exports. They either had a good crop, low demand, or Europe had a high demand for sugar at that time. So, that time period would have been an incentive to expand sugar beet farming.
You would have to know someone with direct knowledge of the geography to know what was there in WWII. Soldier happening upon it probably would not know what the basins were for. But I would say its most likely those basins have been there for a long time.
This is the spot of your picture in Google naps. 50.288469,4.711986 just copy and paste the coordinates into google maps and look for the green arrow.
To me, it appears to be a reservoir systems. The google picture shows everything to be either dry or half empty. But the map view shows tributaries, that can not be detected in the sat view. So I am guessing that a rainy season will fill up the reservoirs and tributaries and then they are used to irrigate the locale crops and farm fields, and will dry out. Something like this, would seem like an old traditional thing to do without modern irrigation methods. They almost look like rice paddies. Maybe something is even grown in them. Are you sure they are fish ponds? The google sat maps shows them either dry or half empty, and not at all like your picture, which is why the appear to be a seasonal thing, but I don't fish, nor do I farm.
I have recently stumbled upon thesi series, and I am surprised that the series is still being worked on, and people are still playing it given its age. I first bought the original Close Combat, A Abridge Too Far, and the version after that, for the Eastern Front.
Since there seems to have been a few iterations of updates, can someone tell me what differences I would notice from when I originally played it, and the newest versions available from matrix games? Have the only changes been the enhancements to movement I can read in the latest patch log? Has the experience of playing the game changed? Basically, what would I notice differently now?
Are there guides available for the newest versions yet? I remember alays getting stuck attacking the bridge with artillery on the other side. Eventually, I got a lucky bazooka shot on it. And in the followup Eastern Front game, I think I gave up playing on it because it just because difficult for me for some reason, probably impatience.
In August of 2004, Zappi, Homba, Bambam887, RedScorpion and MOOXE all pitched
in to create this Close Combat site. I would to thank all the people who have visited
and found this site to thier liking. I hope you had time to check out some
of the great Close Combat mods and our forums. I'd also like to thank
all the members of our volunteer staff that have helped over
the years, and all our users that contributed to this site!