The Department of Fisheries and Oceans is investigating the recent appearance of dead mackerel and sardines near Port Alberni.
The fish washed up along the upper end of Alberni inlet.
Jake Schweigert of DFO said the cause wasn't immediately apparent, "but it is likely due to fish encountering colder and less saline water than they are accustomed to."
Such incidents have occurred occasionally in the past, Schweigert said.
DFO staff are trying to collect samples to test for disease.
