The Jefferson County Sheriff's Office issued a travel advisory for the entire county Thursday. The advisory is in effect until further notice.
Heavy lake effect snow hit the city of Watertown Thursday afternoon.
The roads looked wet, but motorists quickly learned the streets were covered in ice.
The slippery conditions slowed traffic to a crawl on many of Watertown's streets as people behind the wheel got used to winter driving.
No serious accidents were reported in the city.