It could be a Pumpkinseed nest. They aren't colony spawners from what I've observed of them around here. They do nest in shallow water, shallower than Bluegills.

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3/4 to 1 1/4 ac pond LMB, SMB, PS, BG, RES, CC, YP, Bardello BG, (RBT & Blue Tilapia - seasonal).