My old pond and RES pond are side by side, separated by only maybe 100 feet. I built a terrace out into the field (actually a long extension of the dam on the RES pond) quite a long ways specifically for keeping the BH and GSF that I know are in my old pond from getting in my RES pond. In heavy downpours a sheet of water could be coming off the agricultural field and open a pathway for the unwanted fish to migrate. I think a half inch of water is all that is needed for very small fish.

I'm not absolutely sure even the terrace will be absolute control. Some day there may be enough runoff that fish could migrate anyway. But at the very least, just from a numbers game, it should keep the migration to a significantly lower level that what it could have been. If I had just built the dam that the pond "needed" a heavy rain with both ponds overflowing their emergency overflows they would have either almost or actually joined BOW's.

Having had experience with GSF and BH contamination in other ponds and seeing the potential in my brand new RES pond, I went to some length (moved some extra dirt) to prevent it.

One thing about fish contamination, it is much worse to get it early than late. Even if I do get contamination at some later date the desired species will already have established populations and a few unwanted fish will have a hard time getting established to a point of ruining the pond.

John

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