The National Weather Service issued a flash flood warning for McHenry County and surrounding areas that will last from 7 p.m. Saturday evening through late Sunday night.
Widespread showers and thunderstorms are expected to develop Saturday night and continue through Sunday, according to the NWS.
The storms can be capable of heavy rainfall. The NWS expects rates approaching 1.5 to 2 inches per hour at times. Rainfall totals of 2 to 4 inches are possible by Sunday evening. This much rain in a short duration of time over locations that have experienced recent heavy rainfall can lead to additional flash flooding, the NWS said.
The rain will likely lead to river rises in the coming week, especially along the Fox, Des Plains, Pecatonica and Rock river basins.
The Fox Waterway Agency said on its Facebook page that the entire system is closed. This includes the rivers in Zone A, from the Algonquin dam to the Wm.G. Stratton lock and dam near McHenry, Zone B, extending north from the Stratton lock and dam near McHenry to the entrance of Pistakee Lake, and Zone C, which encompasses all 15 of the inter-connected lakes in the Chain O'Lakes.
The system will remain closed throughout the weekend, until Sunday, Sept. 22
According to the Fox Waterway Agency, people may pull their boat out at the nearest available and accessible ramp at no wake speeds. The agency ask that those who do call ahead to make sure it is open.
The Illinois Department of Natural Resources reports that because the ground is very saturated from heavy precipitation last week, and based on the rain forecast, the inflows will increase in the early part of next week.
Gates at Stratton Dam and Algonquin Dam are opened to move as much flow as possible.
In a press release, the McHenry County Department of Health warned residents that flood water can contaminate food and drinking water.
Common water-borne illness symptoms include nausea, vomiting, diarrhea and abdominal cramps, the department said.
"Never allow children to play in flood waters and seek immediate medical attention if you experience these symptoms after exposure to flood waters," the department said in the release.
Flood water exposure does not increase the risk of tetanus, though emergency responders and others affected by floods may be at increased risk for wounds, or may have wounds that can become contaminated, per the health department's release.
Private water wells that have been submerged are considered contaminated and unsafe to drink for cooking, drinking, preparing food, baby formula or brushing teeth. The health department says to get bottled water or bring tap water to a rolling boil for at least 5 minutes before use.
In addition, flooded, non permeable surfaces of indoor areas have to be scrubbed with warm, soapy water.
"If there is sewage backup and the drains are connected to the sewer system, then it can be disposed of by pumping it into the toilet or floor drains," the release said. "Never pump sewage-contaminated water into the yard or into the street."