Not enough hunters have targeted beavers in the past 10 years, a team of farmers south of Ottawa say, so they are banding together to fight a beaver war along the Rideau River.

A rising number of Canadian beavers — this country's national symbol — are gnawing down trees and assembling very sturdy, intricate dams. The dams, built by beavers as heavy as 90 pounds, are blocking water flow and taking important wood.

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Beavers are multiplying in the Rideau River and their dams are causing problems for farmers. (CBC)

One of the reasons, farmers told the CBC's Ashley Burke, is because the reward for hunting the large rodent has plummeted. A "beaver pelt," or dead beaver carcass, used to earn a trapper $150 but some say they are lucky to receive $20 for the dead animal.

"We're losing lots of land. The water backed up three or four acres on both sides of the creek now," said farmer Frank Campbell, who has joined about 60 other farmers to try and control the beaver population.

Some beaver dams can sit about 2.5 meters tall in areas and there are more than a dozen along the Rideau River shoreline. The dams trap water and have flooded thousands of acres of land, killing trees and ruining hayfields.

"It's really hard. Mentally it's a great challenge. When you walk into the fields and can't get your tractor in the field," said sheep farmer John Wodfine, "I mean mine will just sink up to the hubs in the field if I get in there."

Farmers paying big bucks to destroy dams

The trouble caused by beavers has forced farmers to pay a trapper about $1,200 each to tear apart beaver dams. The trapper also sets up traps to kill the beavers.

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Trappers have been hired by a group of more than 60 farmers to destroy beaver dams and kill beavers that are destorying farmland south of Ottawa. (CBC)

One trapper told CBC he has killed 19 beavers, but it has been tiring because the animal keeps multiplying and rebuilding.

The Rideau Valley Conservation Authority has also exhausted many of its resources trying to stop the beavers.

"We do not have enough resources to do this forever for everyone," said Rudy Dyck, "So the conservation authority tries to help where there are severe problems."

The farmers said they hope the waterways eventually clear and land conditions improve as the trappers continue to damage dams and kill off the beavers.