Evansdale, Iowa (CNN) -- Scent dogs used by searchers looking for signs of two missing young girls in Iowa ran around a lake and stopped at the water's edge, the mother of one of the girls said.
Authorities Tuesday were draining Meyers Lake, which is located near an area where the cousins' bicycles and a purse were found hours after they were reported missing Friday.
"It's law enforcement's opinion, let's be 100 percent sure, and the only way to do that is to drain the lake," Blackhawk County Sheriff's spokesman Cpt. Rick Abben told reporters.
The girls -- 8-year-old Elizabeth Collins and 10-year-old Lyric Cook -- were last seen by their grandmother on Friday when they left to go on a bike ride, authorities said.
The FBI brought two dogs to the area to search Monday night, and the dogs were used again on Tuesday, FBI spokeswoman Sandy Breault said.
The dogs used scent pad samples taken from the girls' shoes and picked up a scent trail, but Breault couldn't say what, if anything, it led investigators to.
Misty Cook-Morrissey, Lyric's mother, told CNN that after smelling the scent pads Monday, the dogs ran around the lake and stopped at the water's edge.
Authorities said Tuesday that they didn't know whether the girls had been at the lake.
"We have their bicycles and we have the purse and that doesn't tell me that they've been there, just that those items are there," Abben said.
It could take two to three days to drain the lake to a point where searchers will know if anyone is there, Evansdale Mayor Chad Deutsch said. The lake covers approximately 25 acres.
When Deutsch heard that two little girls were missing in his town, the first thing he did, he said, was to make sure every city asset that was needed was made available to the county sheriff.
The next thing he did was take to the air.
A pilot, he took off in his twin-engine plane and flew over his town looking for any sign of Lyric and Elizabeth.
"It just makes you sick," said Deutsch, who knows both families.
In this town, neighbors know exactly how many people live there -- 4,751 -- and the small community has never suffered through anything like the worrying going on now, the mayor said.
The search remains a missing persons case, authorities said. No evidence exists right now to suggest this is a crime, Deutsch said, but it is a mystery that has the whole community looking for two of their own.
"We just want our girls home," Tammy Brousseau, an aunt to both girls, told CNN's "AC360." "We're bracing for the worst but hoping for the best."
Calls are coming in to a tip line, said Rick Abben, chief deputy for the Black Hawk County Sheriff's Office, and each bit of information is being checked out. Police ask that anyone who may have seen the girls on Friday contact authorities.
Lyric Cook's grandmother, Wylma Cook, said she doesn't believe the girls intended to go swimming.
"I don't think they would have even known the way to Meyers Lake," she told HLN's Nancy Grace on Tuesday.
Lyric's mother, Misty Cook-Morrissey, said the cousins were good about riding just within a few blocks of home.
She echoed Wylma Cook's comments about the girls swimming, given what they were wearing.
"Does it seem likely with her clothes on? I don't think so," Cook-Morrissey told Grace.
Relatives say they have been cooperating with police.
Heather Collins, mother of Elizabeth Collins, told HLN's Jane Velez-Mitchell that if the girls, in fact, were abducted, she would not pass judgment. "We just want our children brought back," she said.
Agents from the FBI and the Iowa Department of Criminal Investigation joined the search on Saturday, authorities said.
Abben told reporters Monday there was no indication the girls were outside Evansdale, which is located about 12 miles southeast of Cedar Falls. Nor was there any indication of foul play, he said.
"It's like they vanished," he told CNN affiliate KWWL. "There's just nothing."
CNN's Martin Savidge, Tristan Smith and Leslie Tripp contributed to this report.