Two ownership groups are selling a Miami River land assemblage with potential zoning for up to 80 stories of commercial space and 1,400 residential units in what amounts to another bet on development potential along the once-polluted waterway.

The Avison Young brokerage firm is marketing properties at 99 SW 7th St., 625 SW 1st Ave. and 66 SW 6th St. in the immediate area. The parcels, adjacent to the mixed-use Brickell City Centre, are known collectively as 99 Riverside. There is no asking price.

The Norman Superstein Trust owns 625 SW 1st Ave. and 66 SW 6th St. Benzol Properties Corp., managed by Bernard and Jerome Herskowitz, owns 99 SW 7th St. For the first time, the groups agreed to sell the three parcels together, Avison Young announced.

Benzol acquired its site for $1.4 million from Brickell M O Living Trust in 2009, according to CoStar. Prior sales data for the Superstein properties was unavailable.

By gaining city approval to close roads between the parcels, a buyer could expand the two-acre site by nearly 33,000 square feet for a total of more than 123,000 square feet of land, according to Avison Young. Aside from the 1,400 residential units, zoning could allow for hospitality, retail and office uses.

Mixed-use projects are becoming a staple in downtown Miami, according to a recent report from CoStar Market Analytics. The report cited Brickell City Centre and the $4 billion Miami Worldcenter as recent examples.

“By constructing mixed-use projects in primary business districts, developers are targeting the dense population of high-income spenders while also providing residential opportunities that can create demand within their own space,” the latest submarket report noted. “Retailers have noticed this trend and intend to be part of the [area’s] fastest-growing urban neighborhoods.”

Existing retail tenants on the 99 Riverside site have termination clauses in their leases that give a buyer flexibility for starting construction on a new development, Avison Young said.

A potential high-rise “will feature unobstructed water and city views, high walkability and convenient connectivity to the rest of the city,” Avison Young’s John Crotty said in a statement.

The shoreline of the 5.5-mile Miami River is home to more than a dozenproposed or existing developments. The river runs through the downtown core and flows past such neighborhoods as Overtown and Little Havana.

A century ago, wealthy residents coveted the riverfront, but the waterway lost its appeal as the downtown and suburbs were developed from the 1970s to the 1990s.

In 1998, the Florida Legislature created the Miami River Commission to improve the waterway and the immediate area. An initial wave of development started there in 2000, with the commission encouraging mixed-use developments to make the river more inviting.