While many noroviruses are spread person-to-person or through contaminated foods, it is important to remember that contaminated water is another good way to move the viruses around. Noroviruses eventually degrade in water, but the rate at which it happens is highly dependent on the water chemistry and conditions.
Earlier this month, swimmers at Thetis Lake in Victoria, British Columbia began falling ill not long after their visit. Over 80 cases were ultimately identified at the public swimming spot, and lab results on samples from some of the sick confirmed the presence of norovirus. Based on who got sick and the water being the most common link between them, it is believed a person with the virus contaminated the lake.
The lake has remained open, though is currently less frequented by visitors, and increased sanitation measures were carried out in the restroom facilities. The local public health authorities are asking people not to swim in the lake if they feel ill, avoid drinking the water, wash their hands before eating, and shower at home after swimming.