Island Health officials are investigating an incident Friday and Saturday where 17 people who swam at Thetis Lake reported falling ill.

Gaylia Lassner took 10 children to Thetis Lake Saturday afternoon to celebrate her son Remy’s 10th birthday. There were about 200 people there, Lassner said Monday.

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The kids were in the water from 4 p.m. until 5:30 p.m., said Lassner.

All of them later got sick starting at about 11 p.m. Sunday and continuing through Monday with a gastrointestinal illness.

Lassner said she’s washed bedding and all the towels that there were in use in the house.

“I’m really gratified that people are looking into this, and whether it’s OK to go back [to Thetis Lake] because we love it there,” said Lassner.

Regular sampling of the lake water over the past four weeks hasn’t shown any bacteria that would sicken people, said Dee Hoyano, medical health officer for Island Health.

“We don’t have an identified organism yet like a bacteria or virus,” said Hoyano.

It’s possible a swimmer who had norovirus, a highly infectious virus, spread it to others through feces or vomit, suggested Hoyano.

Most of those afflicted are recovering quite quickly as is typical for norovirus cases, she said.

Island Health is investigating other sources of bacteriological illnesses and test results may shed more light on the illness on Tuesday.

The beach, a popular draw for swimmers, will not be closed.

Island Health issued a bulletin Monday urging people not to swim if they are ill, not to consume the lake water, clean their hands thoroughly before eating and drinking and shower at home after swimming.

Rehydration is important for those suffering from gastroenteritis, said the bulletin. Anyone seeking medical attention can call 811 for advice.