The usually dark waters of Lost Lagoon in Vancouver's Stanley Park have mysteriously changed colour.The usually dark waters of Lost Lagoon in Vancouver's Stanley Park have mysteriously changed colour. (CBC)

Lost Lagoon in Vancouver's renowned Stanley Park is suddenly looking strikingly different, and has authorities concerned as the usually dark waters of the 500-metre-wide pond have turned a stunning turquoise and nobody is sure why.

The popular tourist spot — widely known as Lost Lagoon but officially called Lost Lagoon Lake — is home to hundreds of animals, including raccoons, swans, ducks and dozens of other bird species.

"It does not seem to be causing any distress to the animals," Vancouver Park Board Commissioner Aaron Jasper told CBC News on Thursday.

"The substance isn't sticking to the birds or other animals so, so far it seems fairly benign," said Jasper.

He said park authorities have taken water samples from the lagoon and expect to have some indication of what's caused the discolouration within a few days.