Rhine river trip

No-one knows! But spring is likely to be better than later - we were on the Danube in May and the water levels were low, but a month later they were unnavigable.

BTW - I realize one cannot predict what the water levels will be but looking for any historical info on how the river levels are in the spring

Sometimes the opposite can happen. Heavy winter snows and warm springs can mean flooding.

I suggest asking an AI bot for a forecast with dates. I would expect there are official sites with historical information that the bot can find and summarize.

There is zero way to know a year ahead. I was there in May 2016 and there was so much water that some of the scenic boats had difficulty docking and there was some minor flooding.

A multi-day long-distance cruise? Or a short 2-4-hour sightseeing cruise? If it's just the short one, no big deal... you can still visit the local towns of interest and take a cruise on the nearby Mosel River, which also has a few castles and is quite beautiful. The Mosel river levels are controlled by locks and less impacted by skimpy rainfall; they are open for cruising even now.

Mosel scene: https://www.mosel-inside.de/en/middle-mosel/cochem.html#gallery38f19924c9-1

I asked Google AI how this year's super el Nino might affect western Europe this winter. The gist of it seems to be a likely heavier amount of precipitation as rain ( or snow in higher elevations). Which may either bring the Rhine's water levels back to normal, or exceed normal and cause some flooding. Only time will tell.