The highest water levels in decades are expected on the Fraser River this Thursday or Friday, according to the Fraser River Forecast Centre.

Heavy rains on the weekend have already led to flood and evacuation warnings in the Interior near Prince George.

The Forecast Centre has officially issued a High Streamflow Advisory for this week for the Lower Fraser River.

Levels at the Mission gauge peaked at 5.9 metres on the weekend before dipping again slightly. David Campbell of the River Forecast Centre said the current projection is that the gauge will hit 6.38 metres on Friday.

That would be higher than the 6.015 that was the peak in 2007, the last year a serious flood threat was forecast. It would mean 24-hour patrols of Langley’s dikes by local emergency officials.

That year, just as water levels began rising, a week of cool air settled over the province and the rate of snowmelt slowed. There was no serious flooding in the Lower Mainland, although local fields, especially outside the dikes, were waterlogged.

In 1972, river levels hit 7.17 metres, and the major flood of 1948 was 7.6 metres.

The forecast may be wrong if weather in southern B.C. brings high temperatures, more rain, or both. That could cause an extra dose of water from nearby mountains and rivers that feed into the Fraser.

“That is a bit of an added piece of uncertainty,” said Campbell.

Meteorologist David Jones of Environment Canada, speaking in a government briefing with Campbell, said that a large low pressure system is preparing to hover over most of B.C. The system is shaped like a wheel, with large “spokes” of cloud and rain that will sweep up from the south.

The next spoke is to sweep in on the weekend, following a brief spike in temperatures, Jones said.

Attorney General Shirley Bond said the province is helping local governments with expertise and heavy equipment. There are two million sandbags in a provincial stockpile, many of them already being distributed, and eight kilometres of gabion diking have been built in Chilliwack in the last few days.

Firefighters who normally would be gearing up for wildfires at this time of year are on call for flooding, instead, Bond said.

- Watch the Langley Advance for further updates over the next few days.