RACINE COUNTY - Looks can be deceiving when it comes to frozen bodies of water.

While it might have been cold enough in recent weeks for a thin layer of ice to form on area waterways, it isn't safe yet to venture out onto them, according to weather experts and local law enforcement officials.

The deaths of three children in recent days, one in Illinois and two in Wisconsin, underscore the concern local officials have at this time of year, before much of the Midwest has fallen into a deep freeze.

So they're issuing a warning to anyone who might think it is safe to venture out onto rivers, lakes and ponds - don't, at least not yet.

"We really haven't had any significant time of below freezing temperatures and that hasn't allowed lakes to freeze to support people's weight on them," said Penny Zabel, a meteorologist with the National Weather Service in Sullivan.

A 9-year-old girl in Naperville, Ill., died Thanksgiving Day after falling through thin ice on a retention pond behind her home, according to the Chicago Tribune.

Two brothers in Manitowoc County died after falling through thin ice Friday while crossing the East Twin River in Two Rivers.

The boys, 13 and 12, were submerged in the freezing river for more than 45 minutes after falling through ice that was less than half an inch thick, according to The Associated Press.

Area waterways need a sustained period of below-freezing temperatures to ensure that ice will be thick enough to support a human being, but there is no reliable rule of thumb for just how long that takes, Zabel said.

It was above freezing every day last week, with temperatures climbing to the upper 30s or low 40s in the Milwaukee area, Zabel said.

So while there might be that thin layer of ice, it's just not thick enough for people to walk on,

Zabel said.

The strength of ice just can't be judged by its appearance, age, thickness, temperature, or whether or not the ice is covered with snow, according to the National Weather Service.

Strength is based on all these factors, including the depth of water under the ice, size of the water body, water chemistry and currents, the distribution of the load on the ice and local climatic

conditions.

There is no such thing as "100 percent safe" ice, according to the National Weather Service.

Every year, the Racine County Sheriff's Department ends up pulling a few people out of the water after they've fallen through the ice, said Sgt. Jim Stratman, a supervisor with the Sheriff's

Department.

It's been a few years since someone has died falling through ice in Racine County, Stratman said. "Ice is very unpredictable," Stratman said. "Ice anywhere in Racine County (right now) is not thick enough to handle people walking on it. Yet there are people riding snowmobiles or four-wheelers out there. Then they end up in trouble."

Things to know about ice safety

- Clear, solid ice at least 2 inches thick is usually sufficient to hold a single person walking on foot. For safety's sake, wait until the ice is at least 3 inches thick and go with a friend.

- Ice will generally be thicker near shore and get thinner as one ventures out further.

- Lake ice is generally stronger than river ice. Springs, lake inlets and outlets, and channels can alter ice thickness.

- Keep children from playing on the ice without adult supervision.

- Because conditions are always changing, the level of danger associated with ice is always changing. You are responsible to make sure ice is sufficiently safe.

Sources: The National Weather Service and the Wisconsin Department of Natural Resources