There's something unusual floating in the waters off Manhattan. (And no, it's not what you're thinking, so please, no mob or radioactive fish jokes.)

Thirty-five years after it was first conceptualized, artist Robert Smithson's (search) "Floating Island To Travel Around Manhattan Island" — a flat barge covered with soil, trees, shrubs and rocks, led by a tugboat — will be doing precisely that, traveling up and down the Hudson and East rivers. The project makes its debut on Saturday, and can be seen through Sept. 25.

"It's a very charismatic project because everyone can relate to an island, we live and work on one," said Diane Shamash, executive director of Minetta Brook, the arts organization that launched the "Floating Island" with the Whitney Museum (search), which is holding a Smithson retrospective through Oct. 25.

Smithson was one of the most significant artists of the 1960s, Shamash said, who was very interested in exploring nature and landscapes, and how they were constructed. He came up with "Floating Island" in 1970 and unsuccessfully tried to bring it to life. He died in 1973 at age 35 after a plane crash.

Smithson was "interested in working outside the walls of the museum," said Eugenie Tsai, who curated the show, which started at the Museum of Contemporary Art (search) in Los Angeles and traveled to Dallas before coming to New York. The Whitney is also hosting a number of events to coincide with the show, including a symposium and a concert.

For the floating island, a 30-foot-by-90-foot flat barge forms the base. It's covered with hay bales, trees, shrubs, soil, and a few rocks borrowed from Central Park. Smithson's original drawing featured a weeping willow and trees native to New York, which the organizers followed, Shamash said. Among the trees are red maples, beeches, and bur oaks. She said the trees will be planted in Central Park afterward.

The island, led by its 45-foot-long tugboat, will be traveling in a U-shaped pattern around Manhattan from 8 a.m. to 8 p.m. every day, and should be visible from many points around the city. It is expected to be in the area of Pier 46, around Charles Street in Greenwich Village near where Smithson lived, Monday through Friday from 4:30 p.m. to 7 p.m., Shamash said.

Tsai said she hoped the project would bring some enjoyment to the people who see it.

"There's a sense of whimsy that I think is really wonderful," she said. "Just to have something out there that's unusual and unexpected that makes people think ... is important."