A runaway hippo in Cape Town has eluded capture by refusing to leave a suburban lake, while another escapee has set up home at a sewage plant, the South African city said Thursday.

The lake-dwelling young male has been promised to a private game reserve but beat a capture team's tranquiliser dart guns by sticking to the water for several days.

"We haven't seen it emerge," said Julia Wood of Cape Town's Biodiversity Management.

The hippo had popped up in gardens and on roads around the Zeekoevlei lake after escaping Rondevlei Nature Reserve when part of the boundary fence was stolen a month ago. But there have been no recent sightings from residents, Wood said.

Another hippo has meanwhile moved into the water pans at a nearby waste disposal plant, where another male spent 18 months after fleeing from a bullying father before finally being removed in 2010.

The city is less concerned about the second escapee as there are not many people around the plant and an electric fence has been set up.

"So our big thing is to focus on the one at Zeekoevlei," Wood said.

Officials will monitor the animal day and night to study its habits and will restart capture efforts once a pattern favourable for darting emerges.

The city has six hippos in the False Bay Nature Reserve. The semi-aquatic animals are known to be extremely violent and can run faster than a human on land.

Another South African hippo, Solly, died last week north of Pretoria in a swimming pool where he got stuck after being kicked out of his herd, and before a crane could lift him to freedom.