Powell and Sakinaw Lakes are stably stratified ex-fjords, which became isolated from the Strait of Georgia approximately 11000 years ago by emerged sills due to post-glacial isostatic rebound. Both lakes contain highly sulphidic relict seawater (Powell 3.0 mM; Sakinaw 5.5 mM) at depth chemically analogous to porewaters of reducing marine sediments. Sakinaw has a very sharp chemocline located just below the oxic/anoxic interface, whereas in Powell, the interface is spread out over 200 m of the water column. Sulphate is present in the oxic part of the water column at much higher concentrations in Sakinaw Lake (up to 65 μM) than in Powell Lake (10 μM), and increases in concentration with depth until reaching the interface, below which it is rapidly depleted. Sulphur oxyanions of intermediate oxidation state (thiosulphate, sulphite, and tetrathionate) are not detectable in either lake. Particulate elemental sulphur was also not found in either lake. High concentrations of reduced iron and hydrogen sulphide result in formation of iron monosulphides and pyrite in the anoxic water columns of both lakes. The presence of these two minerals correlates well with their calculated saturation states. Pyrite precipitates with no apparent monosulphide precursor at depths where dissolved sulphide concentrations are low and monosulphide phases are undersaturated. As sulphide levels increase at greater depths, the waters become saturated with respect to iron monosulphides and particulate FeS species are detected in the water column. The large separation of the oxic/anoxic interface and the chemocline in Sakinaw (~10 m) and especially in Powell Lake (~100 m) relative to that of sediment porewaters allows excellent resolution of these processes.