Bluegills will spawn in shallow sandy bottom areas, from 1' to 3' depth. From what I've seen, they seem to prefer a sand/dirt mix rather than pure clean sand. I've never seen them spawn in gravel, but I don't have much experience with ponds/lakes that are rocky or have a lot of gravel. The country around here is mostly sand and river bottom muck.

I made a couple of flat bottom bays in the pond and the bluegills dug their nests around the shore (3:1 slope) rather than use the flat area that I made for them. It might be because the area is under a little more than 3' of water.

I need to take some pics of the pond today and I'll see if I can get some of their beds.

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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).