What does seem clear is that the project’s critics — environmentalists, human rights advocates and economists — have grown more outspoken and organized. In this part of the country, many homeowners have stenciled “Go Away Chinese” on the sides of their houses, and virtually all the re-election posters for Mr. Ortega have been hit with black paint balls.

When he announced the deal in 2013, Mr. Ortega, a left-wing guerrilla turned pro-business politician, promised that the canal would transform Nicaragua and create hundreds of thousands of jobs, eventually doubling the country’s gross domestic product. Many Nicaraguans, eager for a better future, embraced the idea, and many still do.

But a growing number say the benefits of the deal are not so clear.

Some question whether the canal would even be commercially viable. Few supertankers and massive container ships now afloat will not be able to pass through the expanded Panama Canal set to open soon. And few ports are big enough to welcome those megaships. In the short term, some experts say, the combination of the Panama and Nicaragua canals would lead to overcapacity and price wars.

There are also concerns about the seismic activity in the area, or the many volcanos. Some analysts point to China’s poor record on environmental matters and Mr. Wang’s inexperience in building anything, let alone a $50 billion (some say $80 billion) canal carving through miles of protected areas that are home to many endangered species, including the jaguar, and legally recognized indigenous lands. The little-known Mr. Wang made his fortune in telecommunications, not in construction.

And then there is the 50-mile trench to be dug on the floor of Lake Nicaragua, the largest body of fresh water in Central America — which many fear could end up contaminating, even killing, the lake.

Economists and human rights activists also object to the powers Mr. Wang has to expropriate land at far less than market rates, saying the terms of Mr. Wang’s concession could discourage anyone else from investing in Nicaragua.