Just before 4 p.m. Monday, the toddlers reportedly walked out of a home on San Ramon Court and entered the pool before being discovered by their grandfather, Union City fire Battalion Chief Ronnie Oatis said.
The grandfather pulled them out of the pool and then dialed 911.
Fire personnel responded to the home, where they found the sisters unconscious and not breathing, according to the fire department. Paramedics worked on the toddlers for about 15 minutes and both girls were breathing again as they were transported to area hospitals, Oatis said.
One girl was taken by helicopter to Stanford Medical Center while the other sister was taken by ambulance to Children's Hospital in Oakland. Both were treated and stayed overnight at the hospitals for observation, according to the fire department.
This afternoon, the sisters and their family will be reunited with those who responded to the incident.
"Everybody is looking forward to seeing the two little girls and celebrating them being alive," Oatis said.