The Mekong River's...

English as a Second Language English Vocabulary, Grammar and Idioms
1

“The Mekong River’s Mouth is south of the Cambodian Border.” Are the capital letters correct ?

2

‘Mouth’ does not need capitalisation.

“The Mekong River’s mouth is south of the Cambodian Border.”
“The mouth of the Mekong River is south of the Cambodian Border.”