The National Aquarium in Baltimore won't open its Australian River Canyon exhibit until the spring of 2005, but staffers already have begun to collect the creatures that will live there.

One potential star, now living in the aquarium's off-site care center in Fells Point, is a 3-foot-long crocodile that will eventually grow to a length of 6 to 8 feet.

"You want to get them when they're young and small," rather than try to move them after they're fully grown, explained aquarium executive director David Pittenger.

Other specimens on the acquisition list include grey-headed flying foxes, lizards, turtles, bats, snakes, Australian walking sticks and colorful birds such as cockatoos and lorikeets.

They'll all be part of an exhibit that evokes the Umbrawarra Gorge in Litchfield National Park in the Northern Territory of Australia, complete with a 30-foot waterfall.

While some private sector builders have put off construction projects because of the uncertain economy, the aquarium is sticking to its original schedule for building a $61.8 million addition on Pier 3. Directors have set a groundbreaking for 11:15 a.m. Sept. 5.

Work could have begun even sooner, but the aquarium board decided to wait until after Labor Day - the end of the peak summer tourism season.

"We wanted to have a construction period that covered as few summers as possible," Pittenger explained. "August is our busiest month, so we wanted to wait until it's over."

Designed by Chermayeff, Sollogub and Poole of Boston for the north end of Pier 3, the addition represents the largest expansion in the aquatic museum's 21-year history. Its most prominent feature will be a large glass cube that will rise several stories and enclose the signature exhibit on Australia.

Like the rooftop Amazon Rain Forest exhibit on Pier 3, the river canyon exhibit will be part terrestrial and part aquatic, but the new exhibit will have more water than the rain forest. There will also be examples of Aboriginal art and other information about Aboriginal peoples and their relationship to nature.

A Maryland trek

Part of Pier 3 will be reconstructed to contain a series of free exhibits that simulate a journey through Maryland, from the Eastern Shore to the mountains. The idea, designers say, is to start the visitor experience before people walk in the door. Other proposed improvements include a cafe, gift shop and new main entry to the aquarium.

Northern Australia is an arid environment that gets monsoon-like downpours that flood river beds. It's a sharp contrast to the lush environments of equatorial South America or Africa.

The area chosen for the aquarium's river canyon exhibit is considered part of Australia's Outback, but it's not the flat, desert-like environment that Americans might think of from seeing movies or TV shows, said Mark Donovan, the aquarium's senior director for exhibits and design.

Instead, he said, it's a terrain with geological formations similar to those in the American Southwest, including gorges that "erode from the bottom up, so you get rock falls and overhangs that are very dramatic."

Donovan is one of three aquarium staffers who traveled to Australia for three weeks last fall to explore the area and start making connections with people there who might help them create the exhibit back in Baltimore.

The team searched for an area that would have the combination of land and water features that could make for an engaging exhibit. Staffers originally thought they might find what they wanted in Kakadu National Park, which has 150-foot waterfalls and spectacular rock formations.

Less grand

But the scale turned out to be so grand that the Baltimoreans were afraid they would not have enough space to replicate it adequately in the Inner Harbor. So rather than try to compress what they encountered at Kakadu, they moved on to Litchfield Park and found a gorge with a more intimate scale that was better suited for Pier 3 yet still had all the elements they wanted for the exhibit.

"We fell in love with it," Donovan said. "It was wonderfully intricate, with richly colored rockwork and a wonderful display of flora. The scale of the river, the depth of the river - it was all right there. We knew this area had the potential to do everything we wanted to do."

Donovan and his colleagues shot thousands of photos and hours of videotape to refer to when replicating the river canyon. They already have begun creating scale models.

Pittenger and Donovan said aquarium staffers will work with the Australian government to collect specimens for the river canyon exhibit, but they'll also pursue other sources in the United States and elsewhere, including institutions that raise animals in captivity.

"One of the challenges of the Australian exhibit is collecting the animals, because the country is very protective of its wildlife," Pittenger said. "So we're looking at other ways of collecting what we need."

Unlike reconstruction of the aquarium's oval ring tanks in the 1990s, this project will not require temporarily closing any existing exhibits because it's mostly new construction, but it will involve some rerouting of visitors while work is under way. The ticket booth is being moved closer to Pratt Street for better visibility.

Raising capital

The aquarium is paying for the project through a combination of public and private funds, including the sale of $34 million worth of bonds earlier this year. Its capital campaign has a goal of raising $15 million by the end of 2003, and leaders already have nearly $10 million in hand or pledged.

The construction manager is Aqua Venture, a partnership of Whiting-Turner Contracting Co. and Barton/Malow. Rhodeside & Harwell is the landscape architect. Most of the construction work is due to be finished by the fourth quarter of 2004, giving the aquarium staff time to complete the exhibits and get the animals acclimated for a spring 2005 opening.

The expansion project that begins next month is the largest part of a $112 million master plan that involves improvements to Piers 3 and 4 between now and 2007. Other elements of the master plan include creating a hands-on "family discovery center," tentatively called the Kid Zone, on the second level of the Marine Mammal Pavilion on Pier 4; building a hall for changing exhibits on the lower level of the Marine Mammal Pavilion; and revamping some existing exhibits.

The aquarium will be adding exhibits and programs to keep visitors coming during the construction period. Next spring will mark the debut of Shark Quest, a new way to present information about sharks, and a revamped dolphin show will be introduced in 2004.

The aquarium has acquired a set of jaws from a Megalodon shark - an extinct species that lived more than 1 million years ago and was probably two to three times the size of the great white shark. Current plans call for the jaws, which are 7 feet tall, to be displayed at Shark Quest in a manner that will allow for people to be photographed inside them.

Once all the construction is complete, the aquarium expects to draw 2 million visitors annually, up from 1.7 million in recent years.