The phosphorus distribution in the open waters of the Chesapeake Bay is described. Maxima of soluble reactive phosphorus (SRP) in deep water and total phosphorus in the euphotic zone occur in late summer. The maximum of SRP occurs concurrently with both the seasonal high in productivity in the surface waters and seasonal depletion of dissolved oxygen in the deep water. It is suggested that at this season, phosphate that is produced by remineralization of organic matter escapes precipitation as the ferric salt due to the anoxic conditions and is vertically transported into the euphotic zone where it is rapidly converted into particulate phosphorus by algae. Trophic condition with respect to phosphorus in the open Bay near Annapolis appears to have been unchanged during the period 1938 to 1973.