Dinoflagellates are unicellular, eukaryotic organisms that consist of both photosynthetic and non-photosynthetic species. The approximately 91 known species of bioluminescent dinoflagellates are the pre-dominate contributors to ocean surface bioluminescence. These species are distributed throughout the world, but are generally located in channels, seas, straits, and along coastlines. The bioluminescent properties of dinoflagellates can pose a threat for naval applications. Bioluminescence generated by submarine and SDV operations in coastal areas can result in increased vessel visibility. The initial steps of my research involved testing various chemical agents and physical factors that might be used to mitigate dinoflagellate bioluminescence in situ. I identified formaldehyde as the only chemical compound among many common compounds tested that successfully mitigated dinoflagellate bioluminescence. Formaldehyde was used in the form of formalin, a solution consisting of 37% formaldehyde and methanol as a stabilizing agent. Next, I performed experiments applying shear stress through a stirrer, and used photon counting to determine the extent and time-course of bioluminescence mitigation by formaldehyde in 1.0, 2.5, and 4.6 percent concentrations. Those concentrations were chosen to bracket the formaldehyde concentration commonly used to preserve phytoplankton samples. There was an initial, short-term burst in bioluminescence upon addition of formaldehyde, as formalin, to cultures of the two species before formaldehyde limited bioluminescence, presumably caused by denaturation of compounds in the bioluminescence apparatus. The initial burst lasted 34.6 seconds at 1.0 percent formaldehyde, 9.8 seconds at 2.5 percent formaldehyde, and 8.4 seconds at 4.6 percent formaldehyde for Lingulodinium polyedrum. After the initial burst, bioluminescence output of both Pyrocystis lunula and L. polyedrum was reduced by formaldehyde. For L. polyedrum, the effect was rapid for all concentrations tested, with a 100 percent bioluminescence reduction upon stirring one minute after formalin was added. Bioluminescence continued after administration of formalin, resulting in an afterglow effect for P. lunula. However, L. polyedrum, a species more typical of bioluminescent dinoflagellates found in marine waters compared to P. lunula, did not exhibit the afterglow effect after formalin administration.