Here's a summary from the EPA on some of the things one can do to prevent or manage a toxic algae bloom in their pond.  The accompanying video, which is kind of long for me, goes over these various suggestions (all of which I agree with) and discusses them in more detail.  I also mention a few things that were not included that may be of help such as beneficial microbials.

You can review these recommendations on the EPA website via this link: https://www.epa.gov/cyanohabs