It makes no sense to turn industrial land in the center of Providence’s working port — zoned for industrial use — into a summer playground for families with children. But that is what developer Patrick Conley has tried to do with land he owns between Sprague Energy and Promet Marine Services on Allens Avenue.

In defiance of the city’s zoning regulations, and without first getting permission to do so, Mr. Conley has been holding carnivals, concerts, markets and festivals on a vacant lot at his Providence Piers site as part of his relentless self-promotion for his real-estate and other projects. It’s a bad idea that explains why zoning exists in the first place: Not all uses for land work well together.

Events on the lot, without planning adequately for parking and police, have led people to leave their cars in no-parking zones along busy Allens Avenue, with children crossing four lanes of traffic. Owners of businesses in the area gripe that they have been besieged with people taking over private parking, leading to arguments. Even one of the local strip joints complained to city officials.

This crazy approach almost led to the cancellation of the Puerto Rican Cultural Festival. Mr. Conley’s company sought a variance for the festival, but it was only taken up on July 23, just days before the festival began, on July 25. Since the festival planners said they had already spent tens of thousands of dollars, the Zoning Board was loath to halt the event.

Instead, it gave Mr. Conley permission to continue to hold such amusements until Oct. 31. He may also use the lot itself for spillover parking — a far less disruptive use, though a waste of prime port land — until 2010. At least there are time limits on these approvals.

All this is being played against the background of a fight over changing the zoning of property along Allens Avenue from industrial to a mixed use, possibly so that Mr. Conley can develop residential condominiums on his land.

As we have long argued, there are plenty of other places for developers to cash in by building condominiums and to hold festivals and concerts. What makes this land special is that it hosts a working port — with hundreds of high-paying jobs with good benefits that the region so desperately needs, while stimulating economic activity throughout the region through trade. It would be folly for the city and state to threaten this vital economic engine at a time when Rhode Island needs all the high-paying blue-collar jobs it can get. Anything other than maritime use is a waste of valuable land and the millions of dollars that taxpayers spent dredging the shipping channel.