Imperial Metals Corp., the company that owns the breached pond, is moving water from Polley Lake into Quesnel (kwih-nel) Lake in order to relieve pressure on a wall of debris that formed after the spill.
The provincial environment ministry said water levels in Polley Lake have risen by about two metres.
It said the newly-formed dam is preventing water from flowing out of the lake and authorities are worried the dam will collapse and cause a wash out if pressure on it is not relieved.
Environment Minister Mary Polak said government authorized the company to start pumping after the latest results from Polley Lake suggested water quality is similar to that of samples taken in the 1980s.
A water-use ban on the lake is still in effect, and authorities will be testing water being pumped into Quesnel Lake daily.
Authorities are also restricting access to the area surrounding Polley Lake because of concerns the wall of debris may be unstable and authorities want to make sure no one is in the area if a washout occurs.
Al Richmond, chair of the Cariboo Regional District, said the restriction does not affect any populated areas and no one is being forced from their home.
People have been visiting the area to get a look at the accident site, and they could be interfering with work in the area while putting themselves at risk, Richmond said.
"We know that some folks have been quite curious and have been going in there," he said. "Some folks don't seem to realize we don't want any activity on Polley Lake that might in fact cause that plug to breach."
"If there's a potential breach and you're on Polley Lake fishing for example, you could find yourself in Quesnel Lake pretty quick and the outcomes may not be very pleasant," said Richmond. "I would suggest it would be unlikely someone would survive that type of ride."
Checkpoints and gates have been placed to form a perimeter around the area.
Richmond said it is unclear exactly how much debris is damming Polley Lake, as inspectors have not been able to get close enough to have a look due to fears of getting caught in another washout.
Authorities are not concerned that people exposed to the debris will get sick, he said.
Ten million cubic metres of water and 4.5 million cubic metres of silt was spilled after the Mount Polley tailings pond was breached, raising fears about drinking water, fish stocks and the region's ecosystem.
-By Steven Chua in Vancouver