A 40-year-old woman, from Galashiels, Scotland, has been arrested on suspicion of murder and child neglect and remains in police custody.
Detective Inspector Nick Connaughton from Blackpool CID said: "This is a tragic situation where a young girl has lost her fight for life following an incident at a swimming pool in a hotel in St Annes.
"We are now treating this sad death as suspicious and are investigating just how the child has come into difficulties in the pool."
A spokesman for the 100-bedroom Dalmeny Hotel declined to comment.
More top news
His mother says she hopes being one of the River Island Kids Squad will help dispel negativity and preconceptions surrounding the condition.
Turning wet and windy from the west overnight.
The former shadow business secretary Clive Lewis made the comments at an event backed by Momentum.