(CNN) -- The bodies of two workers at a Gatlinburg, Tennessee, wastewater treatment plant were found late Tuesday afternoon under a wall that had collapsed, sending sewage into the Little Pigeon River, officials said.

Gatlinburg Fire Chief Greg Miller identified the victims as John Eslinger, 53, and Don Storey, 44, employees of contractor Veolia Water North America.

"Employees and officials of both the City of Gatlinburg and Veolia Water are expressing deepest sympathies to the families and are extremely saddened to lose co-workers and good friends," according to a joint statement.

The cause of the collapse remained under investigation.

The wall of a containment basin collapsed Tuesday morning at the Gatlinburg Wastewater Treatment Plant, dumping at least 1.5 million gallons of sewage into the river, according to the state's Emergency Management Agency.

The wall collapse involved an overflow storage basin for liquid waste that commonly inundates the plant after a heavy rain, according to Tisha Calabrese-Benton, a state Emergency Management Agency official.

The basin was not completely full, so it is not known exactly how much sewage was released. Calabrese-Benton said the plant continued to release incoming sewage into the river.

The search for the employees included the river.

A mudslide occurred about one mile from the facility, several hours before the wall collapse, Gatlinburg City Manager Cindy Ogle said. Rain moved through the area overnight Monday.

Crews put up signs to warn tourists away from the Pigeon Forge River, which was already under advisory because of previous concerns about bacteria, according to Calabrese-Benton.

Gatlinburg, a gateway to the Great Smoky Mountains, is a popular mountain resort city. Attractions including whitewater rafting, golf courses, hiking trails, an arts and crafts community and a conference center.

CNN's Aaron Cooper contributed to this report