You probably saw it in person as well, it's called a river :) In Zurich there's multiple places where you can swim in the Limmat, and it takes quite some effort to stay in place - one example is https://images.app.goo.gl/qTASdR51yDTiCk299 (of course you could go without the installation but this allows people to use it that would be afraid of getting carried away ...)

It would be so amazing to live near a river with water clean enough to do this :(

Is there something like this in Berlin?

Could be some settings at the new Wellenwerk that achieve this

The problem with this is that the current is constant. When doing a long set I sometimes accent the arms and the legs alternately over say 200m. Well typically three lengths of arms and one length of kick dominated effort. The thing is the speed does change from one technique to other but moving the water at a constant speed over a short distance doesn't work properly. So it's cute for a little swimming but it's not compelling for serious training. Never mind if you want try doing an individual medley set.

make it a bit longer and have it vary the speed on the position of the swimmer...

Or just have the water channel narrow so the water velocity increases as you move forward.

That's true. The motivation for the swimmer is to not get sucked into the intake. I can hear the coach laughing maniacally as he turns the speed up to 11.

It's called a river. I do a lot if river swimming, but you need to live in a country with clean rivers.

But swimming in lakes is more fun and better for your technique.

They have this at the main Google campus in MTV

"Endless Pool".