Productive vs Un-Productive Water

I am presently working with aquaculture, dealing mainly with 3rd world systems in South East Asia. Many of these systems have a “fertilization” component which involves the addition of manure, thus promoting algal growth with intern provides a food for the fish (such as Indian Carp). It is interesting how “optimal water quality” (i.e. clean/cootie free) equals “unproductive water”. While “unsanitary water” equals “productive water”. I have been reading this FAO publication “Integrated livestock-fish farming systems “ and just found an online copy of it. Interesting reading if you have the time.