Ocean salinity varies slightly but averages around 3.5%. Brackish water would be less than 3% as long as it’s saltier than freshwater, which is limited to 0.05%. Brine, which OP is asking for, is water with 5% or greater salinity. The ocean doesn’t get that high but salt lakes definitely can, the Dead Sea is almost 35% salinity. Also why it’s called the “Dead” sea, FWIW. Maybe you could pickle stuff there.