The Maryland Department of the Environment reports that the Mahogany Tide first observed on 5/19/03 in St. Thomas Creek, a tributary to the lower Patuxent River, (see HAB News from May 21, 2003: "Mahogany Tide blooms in the lower Patuxent River and its tributaries at the end of May.") continued to produce significant concentrations of Prorocentrum minimum as of 5/27/03. Surface water concentrations of P. minimum near the headwaters were 177,660 cells/ml and comparable near the mouth of the creek at 186,570 cells/ml. Despite the cool spring conditions, water temperatures in the main channel of the lower Patuxent River measured at the Maryland DNR long-term water quality monitoring site LE1.3 were average for this time of year. Similar water temperatures were measured in the creek ranging from 16.9 ^oC to 18.4 ^oC. The bloom was present in water with salinities ranging from 4.7 to 8.8 ppt. Dissolved oxygen conditions in the surface waters were supersaturated (>100%) at 18.1 to 18.3 mg O₂/L, a function of the severity of the bloom condition. Additionally, at 1.9m below the surface in the headwaters area, water was hypoxic (well below 100% saturated with oxygen) at 3.7 mg O₂/L. Conditions at 2.9m below the surface near the mouth of the creek were similarly hypoxic at 3.3 mg O₂/L. Such hypoxic conditions would be stressful to most Bay life.