This article describes remote sensing measurements of the distribution of phytoplankton chlorophyll concentrations in the Chesapeake Bay during 1989. The goal of this study was to show that remote sensing from light aircraft can complement and extend measurements made from traditional platforms and provide data of improved temporal and spatial resolution, leading to a better understanding of phytoplankton dynamics in the estuary. We followed the developments of the winter-spring diatom bloom in the polyhaline to mesohaline regions of the estuary and of the late-spring and summer dinoflagellate blooms in oligohaline and mesohaline regions. The instrument we used is an aircraft-borne, visible band radiometer system, NASA's Ocean Data Acquisition System (ODAS). The ODAS instrument package has three radiometers in the blue to blue-green part of the visible spectrum (460 nm, 490 nm, and 520 nm), an infrared temperature sensor, a broad-band (400–700 nm) downwelling irradiance sensor, Loran-C navigation, and a PC for data acquisition. During 1989, 14 flights were conducted in a 19-week period. Two additional missions were flown in conjunction with local shipboard operations for obtaining concurrent radiance measurements and in situ chlorophyll data. The main sources of in situ data used in algorithm development were semimonthly to monthly cruises conducted by the Mainstem Water Quality Monitoring Program of the states of Maryland and Virginia as part of the Chesapeake Bay Program's (CBP) activities. Data for algorithm development were also obtained from shipboard measurements made in an experiment with ODAS and NASA's Airborne Oceanographic Lidar (AOL) to study the suitability of various waveband combinations for recovering chlorophyll concentrations. This article presents the local chlorophyll algorithm we developed using ODAS data and in situ chlorophyll data, interpolated maps of chlorophyll concentration generated by applying the algorithm to aircraft radiance data, ancillary in situ data on nutrients, turbidity, streamflow, and light availability, and an interpretation of phytoplankton dynamics in terms of the chlorophyll distribution in the Chesapeake Bay during 1989.