WILLIAMS LAKE, B.C. - The Cariboo Regional District says about 120 properties may have been affected by flooding along the Chilcotin River and its tributaries in British Columbia's southern Interior.

District officials conducted a flyover of the huge region southwest of Williams Lake on Wednesday in order to determine the extent of flooding that occurred when more than 100 millimetres of rain swamped the area between July 5 and July 9.

Emergency officials say the flooded areas cover hundreds of kilometres, but the hardest hit regions include Big Creek, Nemaiah Valley and the Xeni Gwet'in First Nation.

The say damage to the 120 properties will vary and efforts are underway to determine how long it will take to repair washed out roads and bridges, while 20 ranchers have already reported submerged hay fields and damaged outbuildings.

The B.C. River Forecast Centre is maintaining a flood warning along the Chilcotin River southwest of Williams Lake, but its latest post says water levels have peaked at the one-in-200-year flood level.

Most of the river's tributaries remain at flood stage, although the warning has been reduced to a high streamflow advisory for the Chilko River and Big Creek.

Water levels throughout the river system are forecast to continue receding slowly into the weekend.

Residents stranded by severed roads or bridges will be supported with food and water as required, the regional district says.

It urges affected residents to contact its emergency operations centre to discuss specific assistance.