That 'incredible' smell in Cape Town? A moored ship with 19,000 cows.

When a smell so foul that locals called it “unimaginable” wafted over Cape Town this week, a search for the source of the stench choking the scenic South African tourist destination led to the city's harbour.

Nearly a mile from the dock, Terence van der Walt, a local wine distributor, was stuck in traffic Monday morning when the odor, worsened by the hot summer weather, wafted into his car. Because the scent was so enveloping, it felt pointless to roll up his windows.

“It was so rotten,” Mr. van der Walt said Tuesday, describing his experience. “It would have been green if this was a cartoon.”

After the smell hung over Cape Town for several hours, a team from the local environmental health department discovered the source: a 200-metre long cattle truck registered in Kuwait – with 19,000 cows on board.

The carrier, Al Kuwait, had docked at Cape Town's busy port on Sunday to replenish food supplies during its journey to Iraq from Brazil's Rio Grande port, shipping records show. The animals were on board for more than two weeks.

It was the first time the ship had docked in South Africa, said Jacques Peacock, a spokesman for the national Association for the Prevention of Cruelty to Animals. The organization had thus obtained a court order prior to the ship's arrival allowing inspectors from the group to board the ship and inspect its cargo.

On board, they found a build-up of feces and ammonia in the animals' cramped enclosures, spread across several decks. It had created an “unimaginable” smell, the group said in a statement on Monday.

“This odor is indicative of the terrible conditions in which the animals live,” the report said.

The group has campaigned in South Africa against the transport of live animals by sea and has lobbied the country's government to ban the practice in its waters. Such ships often have poor ventilation and unsanitary conditions, the group said, adding that the animals are at risk of being trampled or injured during journeys over rough seas, and that the ships rarely have a veterinarian on board.

Although the South African government issued new guidelines last year regarding animals exported from the country, Mr Peacock said the SPCA now plans to seek stricter guidelines for vessels coming from other livestock exporting countries.

The ship is owned by Kuwait-based company Al Mawashi, which specializes in the trade and transport of livestock, with offices in Dubai, South Africa and Australia. The company did not respond to requests for comment.

The carrier remained in port on Tuesday and was expected to leave South African waters on Wednesday.

Officials have instructed the local authority that manages the port to ensure that the ship does not pump waste into the port. For his part, Mr van der Walt said he swam in the ocean on Tuesday and found the water to be clear.

In the meantime, although the smell came from outside the city, it was a troubling reminder for locals dealing with another source of filth: the city's crumbling sanitary infrastructure.

Councilors in the mayor's office moved quickly to reassure residents that the latest noxious odor did not come from raw sewage, as happened just weeks earlier when a water pump collapsed in a northeastern suburb.

Last fall, heavy rains damaged pipes in another suburb, sending sewage into rivers and wetlands, said Caroline Marx, director of Rethink the Stink, a water activism group in Cape Town. And since then, the area has suffered about a dozen sewage spills, she said.

Despite the city increasing its sanitation budget, Cape Town is struggling to keep up with rapid urbanisation, Ms Marx said. Outside luxury hotels and affluent suburbs, residents of sprawling shacks without basic amenities often share a water pump and portable chemical toilets.

“The city is years behind where they would like to be,” Ms. Marx said.