The toxic dinoflagellate Pyrodinium bahamense (P. bahamense) produces recurring, persistent summer algal blooms in Old Tampa Bay, Florida, which degrade water quality and are potentially harmful to humans if contaminated shellfish is consumed. As part of its life cycle, P. bahamense produces dormant cysts, which settle to the seafloor, forming seed beds that may initiate future blooms if favorable conditions for germination occur. From August 2015 to September 2016, the U. S. Geological Survey (USGS) and Florida Fish and Wildlife Conservation Commission (FWC) collaborated to conduct seasonal sediment sampling at in Old Tampa Bay, Florida. Sediment cores were collected at three sites. The USGS characterized bottom sediment texture and measured profiles of naturally-occurring radionuclides in the uppermost five centimeters of the sediment column. This information will provide an assessment of sediment accumulation, depositional focusing, and resuspension in relation to the potential impact on the seeding potential of P. bahamense cysts. This data will be used in conjunction with FWC research on the vertical distribution of cyst abundance and viability to estimate the seeding potential of future blooms (Lopez and others, 2015). This project was funded by the Tampa Bay Environmental Restoration Fund. This data release is an archive of USGS field data and laboratory analytical results for the five sampling periods in this study, designated as USGS Field Activity Numbers 2015-329-FA (project ID 15FWR02), 2015-341-FA (project ID 15FWR03), 2016-312-FA (project ID 16FWR04), 2016-327-FA (project ID 16FWR05), and 2016-350-FA (project ID 16FWR06).