NEW YORK—A fleet of handmade art ships was stopped by police in New York Harbor yesterday morning, the New York Times reports. The seven ships were constructed of salvaged materials for a project — "Swimming Cities of Switchback Sea" — by street artist Swoon, and had been floating down the Hudson, headed for New York, for three weeks.

Leaving the 70th Street pier to go around Manhattan and dock in Long Island City, the fleet was spotted by some passengers on the Staten Island Ferry, who notified the police out of concern that the boats were not seaworthy. Police officers stopped the boats and, upon discovering that two of them did not have proper safety equipment, issued summonses.

The artists and organizers of "Swimming Cities" had obtained a permit from the Coast Guard, but the police had not been informed. The Coast Guard escorted the boats the rest of the way to Long Island City, where they docked around noon.