As with many other Pacific iarchaelogical sites, the chronology of the Lapita sites on Tongatapu (Tonga) rests on two bases: a seriation of form and ornament attributes of pottery, and the absolute chronology as determined by radiocarbon dates. Both systems were in disagreement, casting doubt on the reliability of the pottery seriation. The enclosed nature of the lagoon of Tongatapu, coupled with the dissolution of fossil limestone, creates a water reservoir with an apparent age greater than the apparent age of that provided by the open ocean. A lagoon-specific reservoir correction factor was measured using pre-modern reference shells with known dates of collection. When the radiometric dates are corrected using this factor, both chronologies, pottery seriation and radiometric dates, are in perfect agreement. The paper demonstrates how micro-reservoirs impact on ages derived from 14C determinations and shows the need to determine the magnitude of localised variations in 14C.