Justin, 3 quick thoughts come to my mind when first reading your post/question.

First, Do you have fish in your pond?

Second, if so your leaves must not be toxic.

Third, if no fish, get some cheap fathead minnows or Rosey Reds at any pet store and see if they live and reproduce.

My first impressions of the blackwater quotes above instantly seem misleading since the water is "hypoxic" and blackwater comes from low flush, high tannin exposure. Those are not exactly great water quality conditions for fish to begin with. Merely having a "toxic" eucalyptus around wouldn't concern me, as it is likely the chemical reactions in a hypoxic condition that actually releases the leaf toxins mentioned, and not the leaf litter creating the hypoxic condition. Like I said, it is merely my first impression so I am in no way saying my reasoning is right on this.