AbstractProtection of ground‐water resources from the effects of anthropogenic contamination requires definition of the source of water flowing in developed aquifers. Aquifer recharge areas for the confined Magothy and Lloyd aquifers of Long Island, New York, are estimated by using a three‐dimensional model of the Long Island ground‐water flow system and a particle‐tracking algorithm.Aquifer recharge areas under predevelopment conditions are consistent with an understanding of the ground‐water flow system operation. A budget comparison indicated that the recharge occurring in each area as calculated by particle tracking was within one percent of the flow entering that aquifer, according to the water budget computed from the flow model.Aquifer recharge areas for two stressed conditions, one at the present time and the other an estimate for the year 2020, are more difficult to define because of numerous pumped wells. Maximum and minimuitn recharge areas for each aquifer are presented for both present conditions and the year 2020 to bracket the actual aquifer recharge areas. These results also are consistent with the water budgets computed from the flow model.Results indicate that development causes large‐scale changes in flow patterns and the size and shape of aquifer recharge areas. The accuracy of defining recharge areas is limited by the model's representation of local‐scale characteristics of the flow system