Many argue that the reputation is undeserved, as neighborhoods to the north, east and west like Riverdale, Country Club and Pelham Parkway, did not suffer through urban blight. Meanwhile, the South Bronx has been steadily reclaiming its identity for decades.

“For many years we’ve received a bum rap. But we’re just no longer the Bronx that we were in the ’70s and ’80s, and folks are starting to take notice of that,” said Rubén Díaz Jr., the Bronx borough president. “We even have sushi in the South Bronx now. Go figure.”

Affordable housing complexes have been steadily rising throughout the South Bronx, including the Belmont Commons apartments, a nine-story residential development by the South Bronx Overall Economic Development Corporation that opened last week on East 188th Street.

But investors in market-rate housing are on the scene, too, and their interest could reshape the character of the South Bronx. One area that appears on the upswing is the Mott Haven-Port Morris waterfront, a gritty neighborhood with handsome 19th-century manufacturing buildings and a smattering of art galleries, restaurants and boutiques. It is reminiscent of places like Dumbo, Williamsburg and SoHo before they shed their industrial roots and re-emerged as trendy (and pricey) destinations. Quiet even in the middle of the day, the area seems far removed from the bustle of Harlem. But it is just a short walk across the Third Avenue Bridge to 125th Street, which will soon have a Whole Foods Market, a potent symbol of gentrification.

Two derelict sites straddling the Third Avenue Bridge are to be transformed into a mixed-use project with an esplanade and as many as six 25-story towers with 1,600 units of market-rate housing. Construction could begin early next year on the first phase, to open in 2018.

Apartments would rent for around $45 a square foot, about $3,750 a month for a 1,000-square-foot one-bedroom, according to Keith Rubenstein, the president of Somerset Partners, which is developing the property with the Chetrit Group. And the JCAL Development Group is building two multifamily market-rate properties on Alexander Avenue; last year JCAL opened a small four-story apartment house, also market-rate, on Bruckner Boulevard. “You have to be a believer,” said Mr. Rubenstein, who hopes to rebrand the waterfront area as the piano district, in a nod to its piano-manufacturing roots.