Montastrea annularis heads were collected near Negril, Jamaica, along transects from open, normal reef conditions into the mouths of rivers draining the Negril Morass. Corals subject to turbidity (particulate peat and dissolved humic compouonds near rivers, re-suspended reef sediments away from them) were growing more slowly than those in normal circumstances. Surprisingly, corals growing fastest were slowing the most, and the slowest growers increasing growth rate. Linear regression analysis of growth trends over the past two decades revealed stable limit-cycle behavior: change of growth was inversely proportional to growth rate, with a very significant correlation coefficient of -0.92. We suggest that coral growth at Negril is negatively affected by turbidity in freshwater, but locally stimulated by nutrients near the source. Nutrients are likely to be rapidly stripped by dense mats of macrophytic algae which are over-growing corals nearest river mouths.