My pond is a year old and already has lots of GSF including YOY. They most likely came from the two ponds above mine. Likely during the 4" and 6" rainfall events last August. Same with BH.

I suggest building a couple of cloverleaf traps with 1/4" hardware cloth to enable catching smaller fish to see just what is hatching out in your pond. I am tossing out the 1-3" GSF when caught but don't have any expectations of eliminating GSF. Just trying to help getting my BG and RES established then LMB this fall. Once they are established they will dominate over the GSF.

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