About 14 properties close to a major reservoir have been flooded by a breach in an adjoining water tunnel.
A jet of water spouted outside houses next to the Queen Mother Reservoir in Datchet, near Windsor, on Saturday.
Royal Berkshire Fire and Rescue Service said crews were at the scene with a rescue boat after the leak, close to a pumping station.
Thames Water said a breach in a pipe bringing water from the River Thames to the reservoir was responsible.
A spokesman said the adjoining pump had been stopped and the tunnel had been isolated to prevent further flooding.
No-one is thought to have been injured in the flood, but the fire service said at least one person had been rescued by boat.
Thames Water said a row of houses had been left without power.
The flooding affected a stretch of the Horton Road which runs alongside the reservoir.
Thames Valley Police said that a 15ft (4.5m) jet of water had been seen spouting into the air as the underground pipe appeared to have burst open.
A Thames Water spokesman said it appeared to have blown a hole in the road above.
Police said that the flood waters had been around 3ft (91cm) deep but that the level was dropping.
A spokesman said sandbagging had limited most of the water to the gardens with only one house flooded inside.
Firefighters were using pumping equipment to clear the water from the affected house.