(CNN) -- Travel was difficult in parts of northeastern Minnesota and neighboring Wisconsin on Friday, as numerous roads were closed after intense flash flooding that caused millions of dollars in damage and left three people dead.

Flood warnings remained in effect for parts of six counties around Duluth, Minnesota, as well as in Ashland County, Wisconsin, even though waters in some creeks and rivers were receding, the National Weather Service said.

In Ashland County, emergency management officials were discouraging travel because most roads in the county had been compromised by water, according to the National Weather Service.

Minnesota officials have requested federal damage assessment assistance, the first step in deciding whether Gov. Mark Dayton will ask for federal disaster assistance funding, according to the Minnesota Division of Homeland Security and Emergency Management.

The floods followed heavy storms Tuesday and Wednesday that dropped as much as 10 inches of rain on Duluth and neighboring communities.

The flooding washed out roads and bridges, inundated neighborhoods and killed 11 animals at the Duluth zoo.

Efforts to tally the damages are continuing, but preliminary estimates show that recovery will cost many millions of dollars, government officials told CNN affiliate KBJR.

No people were reported dead in Minnesota, but three fatalities were reported in Clark County, Wisconsin. Three people in two cars died Wednesday after crashing on a washed-out road, the state emergency management agency said.

Numerous roads remained closed in Minnesota, and Jay Cooke, Moose Lake and Savanna Portage state parks were closed until further notice due to flooding damage, the Minnesota Department of Natural Resources said.

Recovery will be a long process, KBJR quoted Duluth Chief Administrative Officer David Montgomery as saying.

"This is going to take months in many cases," he said. "It'll take upwards to a year and into next year for some of the major items."

Officials at Lake Superior Zoo were tallying damage there after water surged through the park, leaving 11 animals dead and allowing several others to briefly escape their enclosures.

The zoo moved some animals to other facilities, and some were being kept in quarantine inside the zoo's animal care building during cleanup efforts, the zoo said in a statement posted to its website.

The zoo is planning a volunteer cleanup project this weekend.

Despite the damage, Minnesota officials stressed that Duluth and many state parks in the northwest part of the state are open for tourism and tried to highlight at least one positive effect from the recent storms.

"The waterfalls are incredible right now," state emergency managers said in an update Thursday.