I think what the contours are made from has a bearing on how long they last. I think heavy clay will keep it's shape longer than sand or loam.

A lot also depends on whether the water level fluctuates greatly, if there is considerable wave action, and it also might depend on tha amount and type of fish in the 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).