Officials say lake inversion, and not a chemical or toxpic spill, could be the reason thousands of dead fish washed up along the Lake Erie shoreline over the long weekend.

Ministry of the Environment spokeswoman Kate Jordan says water samples and field measurements have been taken.

Jordan says those measurements didn't show anything unusual in terms of the water chemistry.

She says staff at the site didn't observe any evidence of a spill, run-off or pollution impacting the lake.

Jordan says lake inversion occurs every couple of years when the surface water cools down dramatically, sinks and displaces the bottom layer, which has lower oxygen content - leading to the death of fish habitat.

The ministry expects to receive results from the water samples in the next few days.