Alphie the giant turtle invades Sydney Harbour

The sparkling waters of Sydney Harbour have buoyed the voyages of convict ships, military vessels and now a gigantic 15-metre inflatable turtle.

Early morning strollers in the Botanic Gardens gawked at the colossal creature as it glided past the Opera House, crept under the Sydney Harbour Bridge and berthed at Cockle Bay.

The reef-patterned inflatable sculpture 'Alpha Turtle', affectionately known as Alphie, is in town to celebrate Sydney Aquarium's month-long exhibition of artworks by Great Barrier Reef artist BJ Price.

Inspired by the delicate architecture of coral reefs, the turtle's shell has been printed with Mr Price's well-known 'Alpha' artwork, which is a graphic black-and-white interlocking pattern.

"I like to think of Alphie as a kind of ambassador at large - really large - for the Great Barrier Reef, and what we're hoping for is to inspire people to consider creative ways to address reef health issues," Mr Price said.

As part of the exhibition, sharks and fish will swim around submerged artworks, which have been waterproofed and dropped into the tanks.

The artworks are up for sale with 10 percent of proceeds going to the SEA LIFE trust's reef conservation efforts.

"Hopefully it drives people to be interested in the art exhibition, and in turn, raise awareness of the issues the Great Barrier Reef is facing in the dredging and coral bleaching," an aquarium spokesman said.

Mr Price hopes Alphie will surpass the success of the floating yellow Rubber Duck artwork, which was a highlight of recent Sydney Festivals.

"He's more than just an enlarged bath toy, he'll do a lot more than that ... he'll make people smile but also make people think about their role in helping preserve the largest living organism on the planet," Mr Price said.

Alphie will sit for a month in residency bobbing on the waters at Darling Harbour's Cockle Bay.