Residents of B.C.'s Interior are anxiously watching river and creek levels this weekend, as more rain is forecast with stream levels already high throughout much of the Okanagan.

Environment Canada is forecasting 20 to 50 millimetres of rain for B.C.'s Interior over Saturday and Sunday, and a continued contribution to river volumes from melting snow packs.

On Friday, the B.C. River Forecast Centre upgraded an advisory for the Shuswap River near Enderby to a "flood watch" level.

Gord Molendyk, an emergency co-ordinator in the North Okanagan and Shuswap region, said people living along the Shuswap River need to be prepared for the worst.

"It could come up quickly. So the emergency operations centre is advising property owners in those areas prone to flooding to move your livestock to higher ground," Molendyk said.

"If you're in an area that has flooded before, sandbag your property and we're saying be prepared to evacuate if necessary."

Molendyk says the area near the mouth of the Shuswap River at Mara Lake is of particular concern.

Overflow in Kelowna

Kelowna, which is approximately 90 kilometres south of Enderby, has already experienced a troubling creek overrun this month.

On Thursday, residents of an apartment building in Kelowna had a close call after water from Mission Creek began pushing through a 30-year-old retaining wall and threatened to flood the entire complex.

The city declared a state of local emergency and residents were put under evacuation alert as crews worked through the night to save their homes.

Joe Creron, Kelowna's director of maintenance and operations, said his crews began stabilizing the area at 10 p.m. with truckloads of rock.

"We needed to bring in twice as much as we originally estimated because there was a huge hole here, it was probably five meters deep, seven meters wide," Creron said.

In the end, approximately five tonnes of rock were unloaded for the fill, at a cost in the ballpark of $30,000, Creron said.

But, he said, had the retaining wall burst instead, the damage could have been in the millions.

Dennis Kovacic, whose family built the retaining wall in 1982, said it had done its job until now.

"I've seen water come over the edge but the wall always held up," he said.

Lake level a concern

The creek's level has gone down since Thursday's peak, but officials said the real trouble is Okanagan Lake.

If its level continues to rise, the water will start to back up the tributaries.

"We're at full pool right now, there's discussion we're going up about two centimetres per day. Based on that prediction we've secured some pumps so we can start de-watering downtown as early as Monday evening or Tuesday morning. And of course, everyone will be watching the weather forecast," Creron said.

"We thought the snow pillow was going down and it started to snow last week in some parts so we're in for some fun over the next two weeks, we'll just do our best. When the water subsides, the wall will be assessed," he said.

High stream flow advisories remain in effect for most of British Columbia's major rivers, including the Upper Fraser River, the Upper Columbia River, the Thompson River, the Skeena River and the Cariboo River.

With files from the CBC's Leia Hutchings