Around 200000 people were evacuated on Sunday after Northern California authorities alerted residents that an emergency spillway in the #Oroville Dam, the country's tallest, was in peril of failing.

Authorities said it could release unrestrained amounts of #floodwater on neighboring towns, claiming the worse case scenario is a three-story wall of water being unleashed. This would make it one of the worst environmental disasters in years.

Approximately 150 miles northeast of San Francisco, Lake Oroville is one of #California's biggest man-made water lakes, with a 770-foot-tall dam making it the country's tallest.

Erosion causes grave concerns for experts

Engineers marked out erosion in the dam's secondary spillway on Sunday and ordered the evacuation. Only hours later, frightened and angry residents of #Oroville sat in gridlock traffic in an attempt to leave the locality.

Officials had warned #residents – of Oroville, Gridley, Live Oak, Wheatland, Yuba City, Marysville, Plumas Lake and Olivehurst – that they might only have only an hour to leave.

"Everyone was running around; it was pure chaos," a local resident named Maggie Cabral told CNN partner KFSN. She explained how all of the streets were jammed with cars and people were running about grabbing belongings and frenziedly running out of their homes.

Water levels restored late Sunday

However late Sunday officials said that the #water level had in fact dropped to non-critical levels, alleviating the situation.

The spare Oroville Dam spillway, an embankment scattered with trees, was designed to be the last resort in emergency situations, and was used on Saturday for the first time in history.

This spillway, authorities learned, was also eroding.

The area had been experiencing a massive #drought the last few years, until heavy rain and some snowfall barraged the locale these past few months. The usual annual rainfall is typically 31 inches, but there has been 25 inches since October, according to California Department of Water Resources.

The northern #Sierra Nevada mountains, also facing the wettest season in recent times, channel waters into the lake.

Governor Jerry Brown declared a State of Emergency in response to the situation. “I’ve been in close contact with emergency personnel managing the situation in Oroville throughout the weekend and it’s clear the circumstances are complex and rapidly changing. I want to thank local and state law enforcement for leading #evacuation efforts and doing their part to keep residents safe. The state is directing all necessary personnel and resources to deal with this very serious situation."

There are potential plans to use helicopters to drop rocks into the crevasse to block the water flow and the flooding.

With no rain predicted until around Wednesday, the water has stopped coursing over the spillway, and experts were guardedly optimistic. The evacuation orders are still in place – but people are worried that the storms forecast for the middle of the week could cause a national environmental disaster.