Nope, the entity likely doesn't exist in code anymore. Even if it does, it is implemented with a particle system that doesn't ship with the game. A far better option is to make a new particle system instead. It might be possible to port the original one, but it's tricky, and I don't think there is any automated way to do it.

Sad, but thanks!

Then I will resume my (so far less successful) experiments with the particle system.

Another question about an underwater simulation: Is there any example in a workshop of how to simulate swimming underwater? Or floating in weightlessness?

The locomotion system in my range map lets you turn off gravity, and fling yourself around.

Oh super! I'll try to find (and understand...)

I've looked at the scripts and suspect that they are 'tool_locomotion.lua' and 'quick_locomotion.lua', but unfortunately I'm not enough of a programmer to be able to derive from them what I think my current idea of a movement under water would need, for example:
- The thumbstick as control for forward, right, left
- Buttons on the controller for up and down
or similar actions on the controllers.

Unfortunately, that exceeds my programming skills.

Nevertheless, thank you very much for the tip! Maybe there is one out there who's done anything like this...?