Panic mode switched on for residents of Carnation, Washington, on Tuesday, July 28, after a failure alert siren went off at the Tolt Dam, warning for immediate evacuation. Luckily, it was a false alarm.

"And it was believable, and it was very real," interim Carnation City Manager Bob Jean told King5 news. "We started going through our notifications, and evacuation process."

The loud siren system designed to alert residents of an unlikely event of a failure in the 200-foot high earth-filled dam went off about 11:15 a.m on Tuesday.

According to the Seattle Public Utilities website, "the warning system is automated and monitored by operators in the SPU Operations Control Center 24 hours a day, 7 days a week. Sirens provide early flood warnings and are tested every Wednesday at noon. These tests involve activating the sirens and playing pre-recorded audio messages."

Sgt. Ryan Abbott with the King County Sheriff's Office told Q13 FOX that the alarms were set off accidentally while the technicians were conducting routine checks on the system.

"In the unlikely event of a dam failure, high water in the City limits may exceed a depth of 13 feet within a short period of time. Telephone lines will also be taxed, so contacting local governmental agencies is not recommended. Instead, Carnation residents should heed the siren warnings and follow the evacuation signs away from the inundation area," the utility website stated.

Residents say that they are familiar with the usual test siren and the message played every Wednesday announcing, "This is a test of the Tolt Dam Warning System. This is only a test."

But they say this time it sounded different. The sirens alarmed and produced an alert message that "the Tolt Dam has failed, evacuate the area immediately."

The loud siren and warning message for immediate evacuation created panic among the residents. Roads were blocked as residents scrambled for safety.

"The siren was elongated, went on for like two minutes," Mark Pesanti, a resident in the neighborhood told King5. "I opened the door to hear what they were saying, and it said, 'The dam has failed, evacuate immediately.' So, it didn't take me too long to evacuate."

Another resident told Q13 that fire trucks and firefighters were requesting residents to evacuate the area before they realized it was a false alarm.

"A truck came through saying ' there has been a breach in the Tolt Dam. Get out! Get out! Get out! Get out!" the woman said. "Then another woman came screaming at us and people that were in the river started running. So the word got out that the dam had collapsed."

Jean says the alarm followed by the automated electronic voice warning to evacuate, sounded for about an hour.

Finally, a "clear message" saying "It is safe to return, the dam is secure," was sent once the officials deemed the area is safe for residents to return to their homes.

Fire trucks drove through the area alerting drivers of the false alarm.

The King County Sheriff's Office also sent an alert to the public by tweeting it was a "false alarm."

However, speaking to King5, Jean said that he found a bright side to the unexpected evacuation drill. "I was pleased to see that most people in town took it seriously," he said.

"The reservoir stores 57,900 acre-ft of water to supply 30% of the drinking water for 1.3 million people in the metropolitan Seattle area," the utility website stated.

Dams such as the  Xiaolangdi Reservoir in Luoyang, central Henan province, have opened sluice gates to release upstream water pressure
Representational image. AFP / STR