This is not supposed to be a particular pond, and so it is empty of adjectives or a name.
The poem is not about a special place​​, but the specialness of a moment.

The suddenness accentuates the stillness and focuses our attention on the moment.
The action comes and goes, we cannot hold on to it, just as in real life we never see these frogs jumping in ponds, we only know that it happens.

The sound of water is also the sound of a door closing.
That moment ends and we are left in the present moment.