This phrase is commonly used when describing a skip holed whore who doesn't wash properly. The smell, when she opens her legs can make a man faint if he goes down on her. Even when wearing jeans she is often told to 'CLOSE YOUR LEGS LOVE!'.
Person 1: Did you fuck Steph last night?
Person 2: Yeah mate, I fucked that whore good, but her Salmon Flaps nearly ate me whole. Boy was she smelly! Like a Salmon.