At a time when store closures are accelerating and struggling malls pockmark the country, county commissioners in Florida have approved a plan to build what would be the largest mall in the U.S.

American Dream Miami would also be the most expensive mall ever built, according to Canadian developer Triple Five Worldwide Group of Cos. The 6.2-million-square-foot retail and entertainment complex would cost an estimated $4 billion, Triple Five says.

The cost would include 2,000 hotel rooms, indoor ski slope, ice-climbing wall and water park with a “submarine lake,” where guests could enter a plexiglass submarine and descend underwater.

Edmonton, Alberta-based Triple Five secured zoning approval in May from the Miami-Dade County Commission in an 11-1 vote, and is now in the process to secure environmental and water permits for the 174-acre site.

The project provides a window into the thinking of North America’s largest mall developers as they confront the revolution in the shopping world sparked by e-commerce. They recognize it’s no longer enough to fill malls with stores selling clothing, food, electronics and other merchandise people can more easily buy online.

Rather developers are filling malls with restaurants, rides, trampoline parks, gyms, services and other types of entertainment. This strategy taps into the increasing preference of consumers to spend their money on experiences as opposed to goods.

Indeed, the American Dream Miami originally planned to include 3.5 million square feet of retail space and 1.5 million square feet of entertainment space, said Miguel Diaz de la Portilla, a Miami-based attorney representing Triple Five. Now it’s likely going to do the opposite, with the space mix focusing much more on entertainment.

But just adding modern features and fun amenities hasn’t been a surefire strategy for convincing local governments and financing sources that new malls are needed. Some projects that made it off the drawing board have turned into big money losers or faced lengthy delays.

For example, the American Dream Meadowlands project in New Jersey has become one of the longest-running sagas in the mall-development business. Ground was broken in 2003 on the project, originally named Xanadu, which included a snow dome with ski slopes, an indoor skate park, and an underground aquarium.

But the unfinished project stalled after its first developer ran into financial difficulties. It wound up in Triple Five’s hands in 2013, but the company took years to obtain additional financing. The company says that work has resumed and that American Dream Meadowlands is scheduled to open next year.

Triple Five’s plan for American Dream Miami also faces hurdles. Residents have raised worries about traffic and the environmental impact of the project, while other mall owners have protested possible government subsidies for the project.

Triple Five blames most of the opposition on a coalition of local mall owners who are afraid of the competition. “They launched a campaign of disinformation to mislead the public and decision makers,” said Mr. Diaz de la Portilla.

Triple Five, a privately owned company controlled by the Ghermezian family, owns some of the largest retail and entertainment properties in North America, including West Edmonton Mall in Edmonton, Canada, and Mall of America in Bloomington, Minn.

The debate over American Dream Miami has focused in part on whether there is a need for a new mall in the region. Supporters of the project note that Miami-Dade County’s population grew 10.2% in July 2017 from April 2010, compared with the national average growth of 5.5%, according to the U.S. Census Bureau.

South Florida isn’t representative of the rest of the country, said Zach Winkler, lead of retail for South Florida at JLL. He said the area sees strong tourist arrivals from Latin America and is considered a top retail destination in the U.S.

Supporters also predict the mall will create 25,000 jobs, once opened, partly by attracting 30 million tourists annually. The mall’s submarine ride and other entertainment attractions will be a big lure for this crowd.

But skeptics say that American Dream Miami will mostly attract shoppers from other neighbouring malls rather than tourists who would be more likely to travel to Orlando if they want thrill rides. “I don’t see it competing with Disney World,” said Rafael Romero, vice president of Miami-based real-estate services firm Continental Real Estate Companies.

A big part of the debate is over whether American Dream Miami should get any public subsidies. The South Florida Taxpayers Alliance, a group of mall owners including Simon Property Group, Taubman Centers Inc. and GGP Inc., have lobbied county officials to prevent Triple Five’s project from being funded or subsidized by taxpayer dollars.

The alliance said its aim was to have a level playing field, “where the new employment opportunities promised by the developers of this massive project do not come at the expense of current jobs,” according to its website.

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Triple Five had a history of landing public subsidies for Mall of America and for American Dream Meadowlands.

But Triple Five says it isn’t planning on subsidies for the Miami project. “American Dream Miami will be built by private dollars,” Mr. Diaz de la Portilla said.

The board of commissioners passed a resolution to guarantee that Miami-Dade County doesn’t pay for any part of the construction of the project. The resolution doesn’t prohibit the possibility of subsidies from other sources, such as from the state.