After large crowds gathered at the Lake of the Ozarks over the Memorial Day weekend in defiance of Missouri’s social distancing guidelines, officials in two states urged those visitors to quarantine for two weeks, or until they tested negative for the coronavirus.
The visitors “showed no efforts to follow social distancing practices,” the St. Louis County Department of Health said in a statement on Monday, issuing a travel advisory for people who had been to the popular destination spot.
Video footage from one gathering showed a large crowd of people, most of them in bathing suits and without face masks, at a pool with music blaring overhead and yachts docked at a marina behind them. The videos spread widely on social media over the weekend.
The Lake of the Ozarks, a winding reservoir in the Ozark Mountains of central Missouri, is a tourist destination popular with residents of St. Louis, which is about 150 miles to the east. It draws visitors from across state lines as well.
“It’s irresponsible and dangerous to engage in such high risk behavior just to have some fun over the extended holiday weekend,” Lyda Krewson, the mayor of St. Louis, said in a statement on Tuesday.
“Now, these folks will be going home to St. Louis and counties across Missouri and the Midwest, raising concerns about the potential of more positive cases, hospitalizations, and tragically, deaths,” she said. “It’s just deeply disturbing and threatens the progress we’ve all made together to flatten the curve.”
The Kansas department of health on Tuesday echoed that statement and urged state residents who had been there and did not observe social distancing practices to voluntarily self-quarantine for two weeks.
“The reckless behavior displayed during this weekend risks setting our community back substantially for the progress we’ve already made in slowing the spread of Covid-19,” Dr. Lee A. Norman, the agency’s secretary, said in a statement. “If you traveled to Lake of the Ozarks over the weekend, we urge you to act responsibly and self-quarantine to protect your neighbors, co-workers and family.”
“This is a recommendation, not a mandate,” said Kristi Zears, a spokeswoman for the health department. “We are urging Kansans who traveled to the Ozarks this weekend to do the right thing to safeguard their fellow Kansans.”
She added: “Concerns are certainly raised when we see gatherings like this.”
In a tweet on Monday, Ms. Krewson noted that asymptomatic people can spread the virus and put others at risk, adding that anyone who might have been exposed at the lake should contact the city’s department of health.
There have been at least 12,296 known cases of the coronavirus in Missouri, according to a New York Times database. As of Tuesday morning, at least 694 people had died.
Tony R. Helms, the sheriff of Camden County, which is one of several counties the lake touches, said in a statement on Monday that “there was a record weekend at the Lake of the Ozarks in the middle of a unique situation.”
And while deputies were busy keeping order this weekend, “social distancing is not a crime and therefore the sheriff’s office has no authority to enforce actions in that regard,” Mr. Helms said. “We expect residents and visitors to exhibit personal responsibility when at the lake.”
States have taken different approaches to reopening, and Missouri was among the states pressing ahead. Gov. Michael L. Parson, a Republican, allowed an array of businesses to open their doors beginning on May 4.
Several bars and restaurants on the lake had promoted events ahead of the holiday weekend.
One of them, Backwater Jack’s Bar and Grill, planned a “Zero Ducks Given Pool Party” on Saturday as a kickoff for summer. Ahead of the event, the organizers said the event would operate at reduced capacity, provide temperature screenings and free hand sanitizer bottles at its entrance.
The business declined to comment on Tuesday. Several others that had advertised open hours, events or parties for the Memorial Day weekend did not respond to requests for comment.
The state is now in the first phase of a reopening plan, under which residents are encouraged to stay six feet apart from one another and avoid large gatherings where distancing is impossible.
In its statement on Monday, the St. Louis County Department of Health said employers have asked county officials how they can reopen safely “when social distancing practices are not being followed.”
“This reckless behavior endangers countless people and risks setting us back substantially from the progress we have made in slowing the spread of Covid-19,” Dr. Sam Page, the St. Louis County executive, said in the statement.
The advisory highlighted recommendations that businesses screen employees for Covid-19 symptoms and consider asking them about their recent travels and social distancing efforts.
Dr. Randall W. Williams, the director of the Missouri Department of Health and Senior Services, also urged caution and reminded residents in a statement “that Covid-19 is still here, and social distancing needs to continue to prevent further spread of infections.”
But experts also expressed particular caution about outdoor dining, the use of locker rooms at pools, and crowds in places like beaches.