Do something when particles enter another trigger

Hey guys, I have a Box collider set to trigger. I also have a stream of water particles with collisions turned on.
I want to make the box scale in Y when particles enter the box.

I already figured out how to scale the box, but can’t figure out how to do it when the particles enter. Does anyone have any ideas on how to do this?

Here is the scale script on my box:

public void ScaleUp ()
    		if (transform.localScale.y <= maxheight) {
    			transform.localScale += new Vector3 (0, .1f, 0);

Take a look at Unity - Manual: Triggers module