Rare Chinese white dolphins were spotted near Hong Kong-Zhuhai-Macao Bridge.
The dolphins were spotted by a patrol vessel of Guangdong Maritime Bureau.
Pearl River Estuary is an important habitat of the endangered species.
The Chinese white dolphins are under first-class state protection in China.
Priority was taken to protect the animals during construction of the bridge.
In future, a conservation alliance will facilitate further work.
Since 2011, researchers from Guangdong, Hong Kong and Macao have identified more than 2,000 Chinese white dolphins at the Pearl River Estuary.