"If travelling, be prepared for areas of near zero visibility," said the fog advisory issued Wednesday morning.
The fog is forecast to persist through the morning, and break up in the afternoon, but not clear out entirely.
"What we are looking at is an upper ridge of high pressure which is keeping the situation quite stable," said Environment Canada meteorologist David Wray.
Harbour Air Seaplanes grounded four flights Monday morning, and posted travel alerts on its website for flights to South Vancouver, Victoria Harbour, Nanaimo, Comox and the Gulf Islands.
The B.C. government's E-Comm service warned drivers to take extra care on the roads.
"Slow down and remember low beams are more effective," tweeted E-Comm.
The fog is only about 200 or 300 metres thick, so higher elevations saw sunshine Wednesday, said Environment Canada.