(FORTUNE Magazine) – The latest national craze could be gawking at stingrays, sea turtles, and other exotic underwater species. That's the bet of some 30 U.S. cities that want to construct aquariums. Six -- including New Orleans and Camden, New Jersey -- have already begun. Corporations have been helping with construction costs, which can run up to $100 million. In return, they get gallons of good PR, which is especially helpful to companies accused (fairly or unfairly) of being environmentally insensitive. Occidental Petroleum and Exxon are sponsors of the Texas State Aquarium in Corpus Christi, which will open this summer. Most cities see aquariums as a way to attract tourists, who will spend extra dollars locally, and are happy with breaking even. But it doesn't always work out that way, as taxpayers in Norwalk, Connecticut, found out. Instead of the projected 650,000 visitors last year to the city's new aquarium, only 383,000 showed up. The city had to come up with an extra $2 million to help cover costs. Most cities that built aquariums have happier results. The largest, opened in 1984 in Monterey, California, had 1.7 million visitors in 1989 and is entirely self-supporting. - M.A.