Jeff, if you use PVC, drill some 2/16" holes in the very top of the pipe, and some near the bottom. That will allow the air inside the pipe out, and allow them to sink.

I would set traps on the bottom in 4'-8' of water. In the Spring, when the water is cooler, set them shallower, maybe 3'-6'. I would not set them where any part of the trap was below the thermocline if one sets up in your pond.

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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).