Mzimvubu River or Umzimvubu River is one of the most important rivers in South Africa. It is located in the Eastern Cape Province.

Port St. Johns is a town of about 6,500 people on the Wild Coast in the Eastern Cape province of South Africa. It is situated at the mouth of the Umzimvubu River, 220 kilometres (140 mi) northeast of East London and 70 kilometres (40 mi) east of Mthatha. Port St. Johns was the birthplace of Capital Radio 604.