Rescuers spent fruitless hours searching the Milwaukee River for two sisters who disappeared into the murky, rain-swollen water after the older girl leapt in to try to save her sister.

Authorities were expected to resume the search Monday at daybreak for Tia Woodley, 6, and Temisha Warren, her 12-year-old sister. The two were sucked under the water Sunday near their home.

The girls were playing with their brothers, Jonathan Woodley, 10, and 1-year-old Raygon Warren on a floating pier at about 12:15 p.m. Sunday. Tia, who turned 6 on Sunday, was splashing her foot in the water when she lost her balance, said police Capt. Eric Moore.

Temisha jumped in to try to save Tia, he said, but the girls were swept away by the river, which was moving at about 3 to 4 miles an hour. The girls didn't know how to swim, said Lt. Ron Firnrohr of the Milwaukee Fire Department (search).

"The water was moving extremely fast because the tremendous amount of rain we had," said acting Deputy Chief Brian Glassel. Milwaukee has received about 7 inches of rain, about 4.8 inches above normal for the month.

More than a dozen other friends and relatives watched and waited near where they girls went in Sunday. Later about 30 returned to the spot for a candlelight vigil.

Tamika Woodley, the girls' aunt, said the family was trying to stay optimistic.

"We're trying," she said, struggling to hold back tears. "I just want to see my nieces. That's all I want."

Tia is in kindergarten and Temisha is in fifth grade.

"Temisha's an angel," Woodley said, adding that the oldest child loves to help around the house. "She looked after her sister and brother. She's a sweetheart."

Woodley said the children's mother thought they were at a nearby park.

About 15 officials from the police, fire department and U.S. Coast Guard (search) on four boats and a helicopter helped in the search, Fire Department Capt. Michael Olinger said.

The divers tried to search underwater, but couldn't because of the swift moving water.

"There were two divers with 35 pounds of weight around their waist and the couldn't get down further than two feet," Olinger said.

Firnrohr said the fire department had a heightened alert for this sort of situation Sunday because it was a weekend day with warm weather and a recent heavy rainfall.

Olinger said parents have to keep an eye on their children.

"If it's raining like this and the kids aren't in your eyesight that's the time to keep them close and pull them in. It might have helped in this situation here," he said.