Pesticides are almost always to blame for massive fish kills, he said. They wash from farm fields into rivers during heavy rains.

The province has a mandatory buffer zone between fields and rivers of 15 metres. But to stop fish kills, van den Heuvel said, that zone needs to be bigger and government has to get tougher about enforcement.

"There's never been any serious prosecution of these events. Oilsands companies killed 1,600 ducks and had to pay $3 million, [but] nobody has ever had to pay anything for the millions of fish that have died on P.E.I."