How to make gravity flow?

Question

Unity

Let's take a simple example - water flows and, for example, it has 3 branches at the bottom (that is, like a pipe diverges in a cross, the flow diverges from above, and the flow diverges in 3), certain particles flow in this water (let there be mote balls), based on which branch they swim closer to them and are drawn in, and they are already swimming further along these channels ...
How to do this?
Is it just physics to set up objects and some objects are dynamically flying while others serve as "magnets", or is it scripted to do?
If it is possible examples of this implementation?