A sperm whale's 10m-long carcass was found floating off Jurong Island yesterday.
The species had never previously been found in the waters around Singapore or peninsular Malaysia.
Oil industry worker Jailani Salleh told The Straits Times that he spotted the dead mammal under a jetty at around 7.45am and posted a video of it on Facebook.
Mr Marcus Chua, curator of mammals and birds at the Lee Kong Chian Natural History Museum, was informed and told The Straits Times it was an "exciting find".
The museum will now work to preserve the specimen, believed to be a young adult.
Mr Chua and eight colleagues retrieved the carcass at about 2pm. They have not yet determined the whale's sex or how it died.
The whale appeared to have been dead for several days because of the rot on its body and tongue.
With the help of the Maritime and Port Authority of Singapore, the whale was towed across the West Johor Strait on a three-hour journey to the Tuas Marine Transfer Station. It will be left there for around a week while researchers prepare the skeleton and collect data.
This work will include taking samples of its muscle tissue, which contains precious genetic information, and studying the contents of its stomach. Its skin, internal organs and fat will also be removed.
The museum's scientific officer, Mr Foo Maosheng, said: "By studying its stomach contents, we can possibly tell where it has been feeding and at what depths."
The whale is estimated to weigh between seven and 10 tonnes.
Dolphin researcher Isabelle Tan, 23, from the Animal Concerns Research and Education Society, said: "It is encouraging to know that this species of whale was found in our waters, especially as people often think Singapore has no marine life.
"The sightings are a good reminder that they are there and there is a need to protect the marine environment."
•Additional reporting by Chew Hui Min