<p>A major accidental fire occurred at the Lubrizol plant site in 2019 in Rouen, France. Tons of oils and lubricant additives were vaporized or burnt, transported in a dense cloud of smoke. As unknown compounds were released, the identification of unregulated fire-related markers appeared necessary to evaluate the situation in rivers overflown by the cloud. Surface and underground waters were collected over 1 year to study the spatio-temporal distribution not only of some of the identified fire markers but also of some target compounds (polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and 17 inorganic elements). Untargeted analyses were performed using high-resolution mass spectrometry (GC-HRMS, LC-HRMS) and ultra-high-resolution mass spectrometry FTICR-MS. After chromatogram reprocessing, dozens of compounds could be annotated with different confidence levels and were compared to an in-house database. This was built by adding the accurate masses (<i>m/z</i>) of the listed molecules from the plant stocks and unique <i>m/z</i> collected after the FTICR-MS analyses of soot deposits and liquid leachates collected soon after the accident. Among the molecules matching with the in-house library, 7 from Lubrizol’s stock were identified at high confidence levels and 3 could be possible degradation products. Underground waters were also impregnated by some of the fire markers, suggesting that they may have seeped through the soil. PCBs were not detected in waters, but some PAHs were quantified. However, maximum permissible limits were not exceeded. The waters from the early campaigns concentrated more toxic metals, and Zn occurrence was correlated to the presence of P and B elements, which were potentially emitted in larger amounts during the fire.</p> Graphical Abstract <p></p>