RN:
Sizing sounds about right for a Great Blue Heron.
Since you have a fairly small pond, you may want to emulate Cecil Baird1's heron exclusion efforts. CB1 has had pretty good (although not total) success by placing visible string (80 lbs monfilament - bright colored) around the pond, IIRC just inshore and just offshore, 12"-18" high. This discourages them from wading in the shallowest water that is their hunting zone.
Here are some heron control threads:
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