46 CFR §45.37
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.