The Tennessee Aquarium, said to be the first major freshwater aquarium in the world, opened Friday in downtown Chattanooga. Through several riverine environments in this $45 million complex, visitors can follow the Tennessee River from its source in the Appalachian Mountains through the Tennessee Valley to the Mississippi Delta.

The aquarium displays more than 4,000 specimens of aquatic life, including trout, water fowl, alligators and the 50-pound blue catfish. The Rivers of the World exhibit has re-creations of the flooded forests of the Amazon River, the basin of the St. Lawrence, and other river habitats. Information: Tennessee Aquarium, 101 W. Second St., Chattanooga, Tenn. 37402; (615) 265-0695.

The Oregon Coast Aquarium opens May 23 on 29 acres in Newport, Ore., a 2 1/2 -hour drive southwest from Portland. In a series of indoor and outdoor exhibits, the aquarium traces the journey of a drop of rain from Oregon's Coast Range through forest, river, stream, bog and wetlands to the Pacific.

Information: Oregon Coast Aquarium, 2820 Southeast Ferry Slip

Road, P.O. Box 2000, Newport, Ore. 97365; (503) 867-3474.