46 CFR § 45.37
Salt water load lines
April 15, 2021
Each vessel that operates in the salt water of the St. Lawrence River must—
(a) Be marked with the summer (S), midsummer (MS), intermediate (I) and winter (W) load line marks under §45.77 for salt water; and
(b) Be marked with the letters “FW” above the fresh water marks and the letters “SW” above the salt water marks as described in figure 2.