A method for the determination of dissolved Cr^III and Cr^VI in sea-water is reported based on preconcentration by coprecipitation and electrothermal atomic absorption spectrometry. Coprecipitation with Ga(OH)₃ was carried out to preconcentrate dissolved Cr under optimum conditions. The average recovery was ≈ 98% for Cr^III and <1% for Cr^VI. After reduction of Cr^VI to Cr^III with hydroxylammonium chloride (OHNH₃Cl) total Cr was determined in sea-water, and optimum conditions for this reaction were evaluated. The differential determination of Cr^III and Cr^VI in sea-water was demonstrated by supplementing ‘clean’ sea-water (i.e., [Cr]_total being below the limit of detection) with known amounts of Cr^III and Cr^VI. Recoveries for Cr^III were 95–101%(±3%) and for Cr^VI were 94–99%(±3%). The detection limit for Cr in the preconcentrated sample was ≈ 2 µg l^–1, which corresponds to ≈ 0.02 µg l^–1 in the initial sea-water sample. The proposed method was applied successfully to the analysis of sea-water samples collected at various stations along the French coasts (in Northern France) and in the English Channel transect. It is worth noting that sea-water samples were preconcentrated in the boat immediately after sampling. The findings revealed higher concentrations of dissolved Cr in coastal sea-waters as a result of anthropogenic activities. Conversely, in the French offshore coasts, the concentration of total Cr decreased significantly. Chromium(VI) predominates in oxic open sea-waters with a Cr^VI to Cr^III concentration ratio of 4.