Turlock Irrigation District workers made good on their promise to open the Don Pedro Reservoir on Monday afternoon.
It's the first time the reservoir has been opened in 20 years.
The water began spilling out at 3 p.m.
Turlock Irrigation District which operates the dam says water will be released over the next four days at the least.
Officials made the decision Friday anticipating a series of storms.
The Don Pedro Lake's maintains an 830-feet-high capacity. It has been at 826 to 827 feet.
Stanislaus County Sheriffs have been going door to door warning residents in downstream communities in the Tuolumne River.
As a safety precaution, power is being de-energized along the river from La Grange to the confluence of the Tuolumne and Adan Joaquin Rivers.
No word when power will be restored.
The flood gates are open at the Don Pedro Reservoir in the foothills east of Modesto.
Excessive rain forced the Turlock Irrigation District to open Don Pedro's floodgates to ease the pressure off the Stanislaus County dam.
The lake is 830 feet at capacity and the level has been hovering around 826 to 827 feet in recent days.
The flow of water into the Tuolumne River increased from 11,000 cubic feet per second to 18,000 cfs today. Officials say it could increase to 30,000 cfs.
The spillway is scheduled to be open a minimum 4 days and the effects of downstream communities could be very damaging.
"The amount of water we release will be dependent upon how much precipitation comes in the back", said Calvin Curtain, spokesman for the Turlock Irrigation District.
"So if the precipitation models hold up and all that water comes in then of course the impacts will be larger.
But were expecting the river will rise a few feet probably and some of the low lying areas will see water and will see flooding," added Curtain.
Residents living along the river are packing up and moving out.
In towns like Waterford, east of Modesto, where the river snakes thru neighborhoods,
the Stanislaus County Sheriffs Department sent deputies door to door warning residents to be ready.
Although no official evacuations have been ordered, many like Louise Singleton, who lives just 25 feet from the river, says she is staying.
"We'll see what happens. We'll see what happens," said Singleton.
Power is being turned out to residents who live along the Tuolumne River from La Grange to where the Tuolumne meets the San Joaquin River.