Up to 200,000 people have been evacuated from the area immediately below the Oroville Dam in California in the USA.
Officials feared safety features on the dam, which is the tallest in the USA, would fail sending a 30ft wall of water rushing downstream following an emergency earth slipway attached to the dam suffered significant erosion damage.
Prolonged heavy rain left Lake Oroville less than two metres from the top of the dam, causing water to cascade down the dam’s damaged slipway. This is the first time the lake has experienced such an emergency in its near fifty year history.
Officials are most concerned about the dam's emergency, earthen spillway that began taking on water after water was diverted from the main concrete spillway because of damage.
The authorities ordered evacuations on Sunday for everyone living below the lake out of concern that the emergency spillway could fail.
A change in weather conditions has led to a drop in the water levels but the situation remains critical as up to 10 inches of rain are expected for the California region in the next week.
Lake Oroville is the main reservoir in California, supplying water for more than half the state's 39m residents and for millions of acres of farmland in the leading agricultural state.