What does the salt water joke mean?

The word salt water should be used in Cantonese. If you explain it in formal Cantonese, it means it is not authentic and standard.

My friend, when you say salty jokes here, you should mean those jokes, that is, the yellow jokes in our Mandarin.

Another friend in Guangdong who has the name of salt water girl, you will know what's going on once you Baidu.

There are also orthodox and formal salty songs with salty words, which are native to Guangdong dialect.