Sometime over last weekend, thousands of fish died in three rivers in western P.E.I., the largest kill in decades. Erin Moore/CBC

The Federation of Agriculture says this week's fish kills in western Prince Edward Island are terrible, but it says people are too quick to blame farmers.

Bertha Campbell, the organization's president, has been farming for more than 30 years. She said it's important not to demonize farmers, who are also upset about the fish kills.

"I think they do feel very badly about it and certainly didn't want it to happen and let's wait and see first before we make any judgments," said Campbell.

Earlier this week, dead fish were discovered in three rivers in the western part of the province after heavy rains. Some experts called the fish kills catastrophic and said the most likely cause is pesticide run-off from nearby farm fields.

Campbell said the majority of farmers follow the rules and have buffer zones and hedgerows to try to prevent run-off, but she said farmers can't prevent bad weather.

"It can be really difficult because if you spray your crop and you get a torrential downpour, bad things are going to happen."

Over the last decade, Campbell said farmers have come a long way. She said most have adopted practices that are better for the environment.

Environment Minister Richard Brown said anyone found in violation near the fish kill sites will be charged. And he'll consider increasing the 15-metre buffer zone in high risk areas.

"If I find more that particular areas need more enforcement I will ask for legislative changes in that area," said Brown.

Campbell said farmers are not against changes, but they have to be science-based.

"We have to learn what went wrong in these situations and I don't think it should be a knee-jerk reaction," said Campbell.

Agriculture Minister George Webster said he won't comment on the issue until the fish kill investigation is complete.

The rivers affected included Mill River, the highest salmon-producing river on the Island. Big Pierre Jacque River and Trout River also saw massive numbers of dead fish.

Worst fish kill in decades

Daryl Guignon, a biologist who works for the University of Prince Edward Island, said prior to what he's seen in the last few days, the worst fish kill was in 1972 after chemicals were dumped in the West River. Tens of thousands of fish were killed.

"When I look at this one, It seems every bit as bad as that original one in 1972. As a matter of fact, I don't think I've ever seen so many big fish at one place and from one river as I did in Trout River," said Guignon.

Provincial fish biologist Roseanne MacFarlane agrees the kills have taken a big toll.

"The size of the fish is what's most outstanding about these two fish kills, it's what sets them apart," said MacFarlane.

For every dead four or five pound fish, Guignon said it means about a thousand younger ones are killed too.

"If you have something that kills the fish and all you have left are the big ones, it means there are many, many that just didn't show up. They're in the mud, grass, consumed by predators," explained Guignon.

It's expected to take several weeks for water results to come back, but whatever the cause Guignon said it will take years for the rivers to recover.