A family member immediately called for help.
St John Ambulance, Fire and Emergency NZ and the police rushed to the home.
"Paramedics and firefighters carried out CPR but the child could not be revived," a police spokesman said yesterday.
Police said, at the request of the child's family, her name would not be publicly released at this stage.
Police have provided a report to the coroner on the circumstances of the tragedy.
It was the second backyard swimming pool tragedy in Gisborne this year.
A 16-month-old boy was found by family members in a pool at a property in Collins St in early February.
- Gisborne Herald