Back to understanding the song.

On YouTube there are several versions, one in Afrikaans, with pictures and lyrics. Josef Marais is well represented.

The river is the Mooi, and mealies (or mielies) is maize.

"Mealie-meal is a relatively coarse flour (much coarser than cornflour or cornstarch) made from maize which is known as mielies[1] or mealies in southern Africa, from the Portuguese milho. The Portuguese had originally brought corn from the Americas to Africa." - Wikipedia