[2] The largemouth yellowfish is present in the waters of the Wilge River, reaching quite a large size.

[3] Its sources are about 50 km northeast of Harrismith, at the border with KwaZulu-Natal.

In its upper course the river flows roughly southwestwards from its source, then westwards while bending northwards towards Harrismith, skirting the southern end of the Platberg where there is the confluence with the Nuwejaarspruit from the left.

Further north the Elands River joins its left bank.

It continues flowing in a NNW direction, being joined by the Liebenbergsvlei River from the left, while passing near Frankfort and flowing northwestwards until it finally meets the Vaal at the Vaal Dam further downstream.