The summer water quality testing program at public beaches along Sarnia-Lambton's stretch of Lake Huron has come to a close with all seven locations earning a clean bill of health.

This week's final round of water samples came back from the lab clear of elevated bacteria levels that can result in Lambton Public Health officials posting warning signs for swimmers.

Weekly sampling and testing runs from June to the end of August at Canatara Park, Bright's Grove, Highland Glen, the Ipperwash main beach, Pinery Park and Grand Bend's north and south beaches.

This week's testing was the final round for 2014.

Theresa Warren, a public health inspector, said there were a total of five beach postings this summer, the same number as in 2013.

"It's pretty much what we expect, particularly with the type of weather we had over the past summer," she said.

"Especially in times when we have heavy rainfall and high winds. It causes the bacteria in the lake to be stirred up, and we get high levels when we sample."

Water in the lake can become temporarily polluted for up to 48 hours following heavy rainfall, according to the public health office.

Also, if wave activity has made the lake appear cloudy, bacteria from the lake bottom may have become suspended in the water, increasing the risk of illness.

Just four of this year's beach postings in Lambton were because of high levels of bacteria found in samples.

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Water sampling at Sarnia-Lambton beaches ends for season