Iowa police continued draining a lake Tuesday searching for any trace of two girls who went on a bike ride Friday and have been missing ever since.

Black Hawk County Sheriff's Office Capt. Rick Abben said officials began draining 27-acre Meyers Lake in the northeast Iowa city of Evansdale Monday, and that it could take up to three days.

Authorities previously dredged the lake, but nothing of interest was found.

"The people who were dragging [the lake] were confident ... there was no one in there. However, it is our opinion we should be 100 percent sure," Abben said. "If we find out they are not in there, we can put our efforts totally somewhere else."

Lyric Cook-Morrissey, 10, of Waterloo and her 8-year-old cousin Elizabeth Collins of Evansdale were last seen Friday afternoon, when they left their grandmother's Evansdale home on a bike ride. The girls' bikes and one of their purses were found later Friday on a nature trail that runs along Meyers Lake.

One Saturday and Sunday roughly 1,000 community volunteers searched a 12-mile radius of where the girls' bicycles were found. Nothing was found indicating what happened to them.

The girls' parents could not be reached for comment Tuesday. On Monday, Misty Cook-Morrissey, Lyric's mother, told reporters the family is trying to stay strong.

"It's very difficult, but we're trusting in the Lord and just trying to be patient and let everybody do their job, and we're doing a lot of praying," Misty Cook-Morrissey, Lyric's mother, told reporters.

"I have hope because of the Lord's great love," Heather Collins, Elizabeth's mother, said at the vigil.

On Tuesday, Collins told ABC's "Good Morning America" she fears the girls may have been kidnapped.

"I want to say to [the person responsible] that my husband and I have forgiven them," she said. "God has forgiven them already. So we have forgiven them and we just want our children back safe and sound. That's all we want. We don't even want to know who the person is."

Authorities said there is no evidence of foul play in the girls' disappearances. "We have two missing girls, and we have no idea why," Abben said.

The FBI has been assisting in the investigation. The agency is providing search dogs to police and is helping local law enforcement get photos of the girls online and on local billboards.

Elizabeth is described as a white female, 4'1" tall, 65 lbs., with sandy hair and blue eyes. Lyric is white, 4'11", 145 lbs. with brown hair and blue eyes. Anyone with information on the girls' whereabouts is asked to call the Tip Line at (319) 232-8862. According to the Waterloo Courier, there is a reward for the safe return of the children.

CASE PHOTOS:

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  • Lyric Cook-Morrisey Elizabeth Collins

    Lyric Cook-Morrisey (left) and her cousin, Elizabeth Collins, have been missing since July 13.

  • Lyric Cook-Morrisey And Elizabeth Collins

    Lyric Cook-Morrisey (left) and her cousin, Elizabeth Collins, were last seen July 13, when they left their grandmother's Evansdale, Iowa home and went on a bike ride. The girl's bikes and one of their purses were later found along a nature trail that runs along Meyers Lake.

  • Misty and Dan Morrissey speak to the media near Meyers Lake where their daughter Lyric Cook-Morrissey, 10, and Elizabeth Collins, 8, disappeared last Friday, Tuesday, July 17, 2012, in Evansdale, Iowa. The girls' bikes were found Friday afternoon near a bike trail at the edge of the lake. (AP Photo/Charlie Neibergall)

  • Elizabeth Collins

    Eight-year-old Elizabeth Collins.

  • Lyric Cook-Morrisey

    Ten-year-old Lyric Cook-Morrisey

  • Dan Morrissey leans on a tree near Meyers Lake where his daughter Lyric Cook-Morrissey, 10, and Elizabeth Collins, 8, disappeared last Friday, Tuesday, July 17, 2012, in Evansdale, Iowa. The girls' bikes were found Friday afternoon near a bike trail at the edge of the lake. (AP Photo/Charlie Neibergall)

  • Elizabeth Collins And Lyric Cook-Morrisey

    Elizabeth is described as a white female, 4'1" tall, 65 lbs., with sandy hair and blue eyes. Lyric is also a white female, 4'11" tall, 145 lbs. with brown hair and blue eyes. Anyone with information on the girl's whereabouts is asked to call the Tip Line at (319) 232-8862. According to the Waterloo Courier, a reward for the safe return of the children is available.

  • Black Hawk County chief deputy Captain Rick Abben speaks during a news conference about the investigation of missing children Lyric Cook-Morrissey, 10, and Elizabeth Collins, 8, who disappeared last Friday at Meyers Lake, Tuesday, July 17, 2012, in Evansdale, Iowa. The girls' bikes were found Friday afternoon near a bike trail at the edge of the lake. (AP Photo/Charlie Neibergall)

  • Law enforcement authorities collect possible evidence near Meyers Lake where Lyric Cook-Morrissey, 10, and Elizabeth Collins, 8, disappeared last Friday, Tuesday, July 17, 2012, in Evansdale, Iowa. The girls' bikes were found Friday afternoon near a bike trail at the edge of the lake. (AP Photo/Charlie Neibergall)

  • Law enforcement authorities collect possible evidence near Meyers Lake where Lyric Cook-Morrissey, 10, and Elizabeth Collins, 8, disappeared last Friday, Tuesday, July 17, 2012, in Evansdale, Iowa. The girls' bikes were found Friday afternoon near a bike trail at the edge of the lake. (AP Photo/Charlie Neibergall)

  • Misty and Dan Morrissey walk to speak to the media near Meyers Lake where their daughter Lyric Cook-Morrissey, 10, and Elizabeth Collins, 8, disappeared last Friday, Tuesday, July 17, 2012, in Evansdale, Iowa. The girls' bikes were found Friday afternoon near a bike trail at the edge of the lake. (AP Photo/Charlie Neibergall)

  • Law enforcement authorities look for possible evidence at Meyers Lake where Lyric Cook-Morrissey, 10, and Elizabeth Collins, 8, disappeared last Friday, Tuesday, July 17, 2012, in Evansdale, Iowa. The girls' bikes were found Friday afternoon near a bike trail at the edge of the lake. (AP Photo/Charlie Neibergall)

  • Law enforcement authorities in kayaks search Meyers Lake where Lyric Cook-Morrissey, 10, and Elizabeth Collins, 8, disappeared last Friday, Tuesday, July 17, 2012, in Evansdale, Iowa. The girls' bikes were found Friday afternoon near a bike trail at the edge of the lake. (AP Photo/Charlie Neibergall)

  • Local residents sit on a park bench near Meyers Lake where Lyric Cook-Morrissey, 10, and Elizabeth Collins, 8, disappeared last Friday, on Tuesday, July 17, 2012, in Evansdale, Iowa. The girls' bikes were found Friday afternoon near a bike trail at the edge of the lake. (AP Photo/Charlie Neibergall)

  • Sarah Staebell ties pink ribbons for Lyric Cook- Morrisse, 10, and Elizabeth Collins,8, missing from Evansdale since last Friday, on light poles along Lafayette Street in Evandale Monday, July 16, 2012. The two girls have been missing since leaving their grandmotherÂ's house Friday afternoon in Evansdale. Their bikes were found Friday afternoon near a bike trail at the edge of Meyers Lake in Evansdale. (AP Photo/Waterloo Courier, Brandon Pollock)

  • An off-duty Cedar Rapids police officer searches the underbrush for clues to the disappearance of Lyric Cook-Morrissey and Elizabeth Collins along the bike trail around Meyers Lake in Evansdale Monday, July 16, 2012. The two girls have been missing since leaving their grandmotherÂ's house Friday afternoon in Evansdale. Their bikes were found Friday afternoon near a bike trail at the edge of Meyers Lake in Evansdale. (AP Photo/Waterloo Courier, Brandon Pollock)

  • This undated photo provided by Black Hawk County police shows 10-year-old Lyric Cook-Morrissey who, along with her 8-year-old cousin Elizabeth Collins, has been missing since Friday afternoon, July 13, 2012. The girls were last scene Friday afternoon leaving their grandmother's house. (AP Photo/Black Hawk County Police via Waterloo Courier)

  • Elizabeth Collins

    This undated photo provided by Black Hawk County police shows 8-year-old Elizabeth Collins, who, along with her10-year-old cousin Lyric Cook-Morrissey, has been missing since Friday afternoon, July 13, 2012. The girls were last seen Friday afternoon leaving their grandmother's house. (AP Photo/Black Hawk County Police via Waterloo Courier)

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