If that natural spring is inside of the pond basin, then there's the possibility of the pond surface water not getting much higher than the spring. Then again, it might be like my pond. When water table levels are high, the water in the pond is 8' or so higher than the spring. But, when water table levels are low, then my pond is only about 1' higher than the spring.

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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).