(CNN) -- After treading water for about 20 hours, a 4-year-old girl and three others were rescued Sunday by Coast Guard crews off the Florida Keys, though an 80-year-old woman drowned before she could be reached.
The Coast Guard said Sunday in a news release that the rescue occurred Sunday morning near Marathon, which is roughly halfway between Key Largo and Key West.
Those saved were among a group of eight that had been on a boat that sank not long after noon Saturday.
The elderly woman was among those on the boat, but the Coast Guard reported that she never surfaced.
Three other members of the group were picked up by a passer-by.
"Not all" of the boaters were wearing life jackets, according to the Coast Guard's initial report.
A crew based at the Coast Guard's Marathon station brought the four rescued boaters to emergency medical workers waiting at a nearby marina and dive center.
They were assisted by members of the Florida Fish and Wildlife Conservation Commission, which is investigating the incident.