What: Ocean Journey, Denver's $93 million aquarium, which opened June 21

Why: To witness the next wave in aquatic showplaces. Rather than highlight species or portray mini-environments, Ocean Journey takes visitors on two great river trips--on the Colorado River and on Indonesia's Kampar River. Think of it as aquarium-as-narrative.

Two rare Sumatran tigers top a cast of 15,000 fish, mammals, birds and more than 1,000 plants that live behind acrylic viewing panels in the facility. There are flash floods, blasts of cold mountain air and tropical mists. Dozens of animal sounds, from elk and coyotes to orangutans and sea lions, are programmed in an audio track not to repeat in the same order for four years. Along the way, there are interpretive guideposts, but to reduce signage Ocean Journey gives each visitor an excellent 32-page "Field Guide" to the exhibits. It's a nice souvenir. Knowledgeable volunteers are stationed throughout.

Colorado River Journey. Halfway through this exhibit, my 14-year-old daughter and I were startled by fierce thunder and lightning. Suddenly thousands of gallons of water crashed through a narrow desert canyon, spraying us and other unsuspecting visitors. In the high desert, flash floods, sometimes fatal, occur after rainstorms. At Ocean Journey, a flash flood happens every two minutes. "Ocean Journey is the story of moving water and the power of water," explains Jon Mann, director of education.

The Colorado River exhibit begins at tree line along the Continental Divide. Air conditioning keeps summer temperatures chilly here, as it is at 12,700 feet. Icy water cascades down mock granite formations into pools of huge trout, including rainbows, browns and Colorado's official state fish, the greenback cutthroat, with its bright red spots and gills. The exhibit ends on the Mexican border at the Gulf of California in a kaleidoscope of 6,000 tropical fish and 187,000 gallons of salt water. In between, there is a wetlands with river otters and beaver dams, a reservoir with tough-looking northern pike and three endangered Colorado native fish (the humpback chub, bonytail chub and Colorado pikeminnow, all driven to near-extinction by introduced predators).

Indonesian River Journey. On the other side of the world--just a few steps away--the Kampar River tumbles down the slopes of the Barisan Mountains to the South China Sea. We walked among giant tree trunks under a rain forest canopy of live vines, then into a mangrove swamp with fish like the bumblebee catfish, Siamese flying fox and tinfoil barb whose names match their strange looks.

Bali and Java, a pair of year-old Sumatran tigers, inhabit their own 5,000-square-foot, multilevel space with a 30-foot waterfall and a pond. Some Denverites question whether the tigers belong in the aquarium. Ocean Journey says the Sumatran tiger is endangered--only about 500 exist--and that educating the public about them will help ensure the species' survival. In the wild, these cats spend a lot of time in the water to stay cool.

One of the oddest fish is the two-inch blue-spotted jawfish: It swims vertically, using its mouth to carry tiny pebbles to make its burrow. I like the big, sad-eyed Napolean wrasse, a fish that grows to 400 pounds and lives 100 years; its puffy lips are considered a delicacy by some Asians. The Kampar River exhibit ends at Depths of the Pacific, with three kinds of sharks, rays, a zillion tropical fish and big jellyfish (properly known simply as "jellies," we learned, since as invertebrates they are not really fish).

Fact Sheet. The 106,500-square-foot Ocean Journey holds a million gallons of fresh and salt water--about half the size of Baltimore's National Aquarium.

Environs. The nonprofit Ocean Journey is on the western edge of Denver's lively downtown. A bike path and trolley pass the aquarium, which is a 10-minute walk from the Denver Children's Museum. From Ocean Journey's outdoor Riverside Cafe, you can see and hear Six Flags Elitch Gardens, an amusement park just across the narrow South Platte River.

Ocean Journey is in US West Park, 700 Water St. Admission: adults 18 and up, $14.95; youths 13-17 and seniors 65 and up, $12.95; children 4-12, $6.95; 3 years and under free. To beat the crowds, visit later in the afternoon. 303-561-4450; www.oceanjourney.org.