I would guess the 2-3 inches is re-saturation of the surrounding soils. Is your watershed large enough to support the increase in water volume? If you pumped in water from a creek that runs year round, you likely pumped in unwanted fish species, unless a good filter was used.

Since you said the expanded area was not compacted, you may be better off long term to drain it, let it dry some and compact before re-filling with filtered water from the creek.