Wildlife experts attempting to rescue the dolphin, which is a protected species in China, said its health had deteriorated noticeably during the last 10 days.
The mature dolphin, which was estimated to be around 30- years-old, swam into the Baisha River, a tributary of the Pearl River in Jiangmen, on February 1 and died last night.
It is thought that the dolphin may have been suffering navigation issues due to its age, state-run Xinhua news agency reported.
"Chinese white dolphins are social animals, so elderly individuals can easily get lost if they have navigation or hearing problems," said Fang Liang, a researcher with the School of Marine Sciences, Sun Yat-sen University.
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Each year, Guangdong reports two to three cases of senior white dolphins mistakenly entering freshwater rivers.
Chinese white dolphins can be found in just a handful of coastal areas.
There are about 2,000 at the mouth of the Pearl River.