A two-dimensional Lagrangian particle trajectory model is described and used to study how surface currents transport particles and, by analogy, plankton in Chesapeake Bay, United States. It is shown that persistent patches of high particle concentration develop in well-defined regions along the eastern shore and in the lower reaches of some western shore tributaries due to a combination of passive accumulation of particles in areas where the flushing rate is low and convergence. In the model the highest particle concentrations in the Chesapeake consistently develop in the lower bay (latitude 37.1¿--37.7 ¿N) in two specific regions near the shore of Cape Charles where convergence and downwelling occur. It is shown that one of these is associated with a strong and persistent, residual cyclonic eddy located over an abrupt change in bottom topography. Recent bay wide field surveys reveal that various planktonic groups, including phytoplankton, zooplankton, and bay anchovy eggs and larvae, have maximum abundances in the vicinity of this eddy. It is argued that these convergent areas are important features that have a strong influence on plankton distributions and that they provide consistently high food concentrations for higher trophic levels. ¿ 1999 American Geophysical Union