The Galveston Police Department said it happened at a home on Colony Park Circle near 69th Street and Seawall Boulevard.
Galveston police said the 23-month-old was pulled from the water by a caretaker.
The small child was taken to the hospital, where she died on Friday morning.
Investigators said the incident appears to be an accident.
SEE MORE: 3 tips to keep your children safe around the pool this summer
3 pool safety tips to keep your children safe this summer