PRINCE RUPERT, B.C. - A boil water advisory is in effect for the 12,000 residents of Prince Rupert, B.C., following extreme weather this year.

The city says unacceptable levels of the parasites cryptosporidium and giardia have been detected in water samples, and seniors, children and people with compromised immune systems are at higher risk of infection.

Residents are directed to boil water continuously for one minute prior to drinking it and the city says home water filtration systems are not considered effective in restoring water quality in this instance.

It says this year's dry summer followed by a storm surge pushed debris into the water supply, making it undrinkable.

In August, the city applied for funding to implement a two-phased water treatment system and replace a submarine line carrying potable water from two nearby lakes.

The project will also see the city's 100-year-old dam replaced.