If a person were to add chemical fertilizer to a pond to spur an algae
bloom, then to harvest the algae for use as compost, would that still be
considered "organic gardening"?

Don't you kind of answer your own question here? Organic Gardening is, by
definition, NOT using chemicals. (Using common vernacular here -- obviously
everything in the garden and such has a chemical nature.) If one uses
chemical fertilizers then that would pretty much immediately negate the
organic aspects. Granted, it might work wonders and all but finding a
natural means would be preferred of course.

Considering how easily algae takes hold of any body of water, I'd have to
wonder why anyone would feel the need to resort to chemicals to encourage
its growth. Hmmmm....

James