Zep, you beat me to it. I've seen too many of the overflow pipes plugged with junk like yours was plugged, and it's flat out too dangerous to try and unplug them when the water is high.

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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).