WILLIAMS LAKE, B.C. - Officials in British Columbia's southern Interior said an overflight of the Chilcotin River and its tributaries could give a better picture of the severity of flooding that has swamped the region since heavy rains hit last weekend.

A flood warning posted Monday by the River Forecast Centre remained in effect Wednesday, although the warning had been downgraded to a high streamflow advisory for two tributaries; the Chilko River and Big Creek.

Cariboo Regional District spokeswoman Emily Epp said levels on the Chilcotin River were expected to begin receding soon.

“We were kind of expecting the crest of the flooding (Tuesday) or overnight and hopefully receding over the next couple of days,” she said.

“However because it is ... not a spring freshet event, it really will depend on the rain events that we see.”

The River Forecast Centre said as much as 100 millimetres of rain had fallen in the region southwest of Williams Lake between July 5 and July 9, while the weather office was calling for as much as 20 mm of rain by Wednesday night, possibly accompanied by thunderstorms or hail.

“We are seeing flooding on properties and ranches as well as road access cut off for some people in that area,” said Epp.

The regional district had heard from about 20 ranchers and Epp said flooding was likely affecting many more people and properties, “particularly hayfields and that kind of thing.”

The district “definitely” expects to hear from more than two dozen property owners, said Epp, because the flood-stricken region covers hundreds of kilometres and includes the community of Big Creek, the Xeni Gwet'in First Nation and the Nemaiah Valley.

“It is such a large area we don't quite have a sense yet of who, and how many people have been impacted,” she said.

“Most people still have working phones, so we have heard from several and word of mouth travels quickly through that area but hopefully with our flight ... we will be able to connect with most, if not all, of the residents to get a better sense of their situation.

An advisory from Interior Health says well- or river-water systems impacted by flooding should not be used and Epp said the regional district was delivering potable water to some ranches, but the emergency operations centre wants to hear from more people in order to assess need.