MILWAUKEE (AP) — Instead of kayakers and tour boats, the summertime scene on the Milwaukee River has taken on a solemn tone this week during the Republican National Convention: Around-the-clock patrol boats, some with heavily armed officers.

Security planners have had to contend with the winding waterways through Milwaukee near the Fiserv Center RNC convention site, along with securing downtown streets. Roughly half a dozen police departments, along with state and federal agencies, have boats patrolling the river 24-hours-a-day until the convention ends this week.

“They’re committed to working those long shifts, throughout the days and nights,” U.S. Coast Guard Lt. Joe Neff said. “They’ve been all on board for making sure public safety is priority.”

Associated Press journalists were allowed on board a 29-foot U.S. Coast Guard boat Wednesday to observe. The boat, typically used for search-and-rescue operations, traveled near the secure zone of the convention site via Lake Michigan and the river that empties into it.

A large section of the river has been shut down to commercial and recreational traffic this week, with very few exceptions, like residents who live on the river. Within an hour, the Coast Guard boat had passed vessels from Milwaukee police, state conservation wardens and a heavily armed specialty Coast Guard tactical force in camouflage gear.

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The patrols are part of a massive security plan that Milwaukee police, the U.S. Secret Service and others have been detailing for more than a year. Security around former President Donald Trump, the Republican presidential nominee, has been especially tight in the wake of last weekend’s apparent assassination attempt.

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“There is no higher level of security that can be invested in events such as this,” Milwaukee Police Chief Norman Jeffery told The Associated Press Wednesday.

So far, no major incidents have been reported on the water during the convention, according to the Coast Guard.

Patrol boats typically depart from a Coast Guard facility south of downtown on Lake Michigan, before turning into the mouth of the channel where the river begins. Speeds are then slowed to 5 mph and boats pass by the restaurants and converted warehouses of Milwaukee’s Historic Third Ward on the way to the secure zone.

The boats are tasked with monitoring Milwaukee’s downtown bridges and keeping unauthorized people and vessels out of the secure zone.

They are also on the lookout for anything suspicious.

As the Coast Guard vessel traveled near the downtown security zone, the crew spotted something mysterious floating in the water. They turned the boat around and fished it out, discovering the object was only a red and gray nylon tarp that had been rolled up and posed no threat.

Coast Guard officials said the help from other agencies this week also means they can keep up their usual public safety duties.

“Yes, we’ve got the national security event here, the RNC. That doesn’t mean we’re ignoring the rest of our normal mission — search and rescue,” said Coast Guard Lt. Phillip Gurtler. “We still have the coverage that we need.”