Bob Crawford, president of the Cowichan Valley Agricultural Society, said he has seen more than 100 swans in just one field, grazing on the grass, causing flooding and soil damage.
"Every time these birds get in on a field that's grazed, it delays the cutting of crops by seven days," he told On The Island's Gregor Craigie.
"Hence the shortening of the harvest time, which can mean only two crops, rather than three, or even just one crop, leaving the farmer not enough feed for his livestock."
In the case of ducks and Canada geese, farmers can allow hunters on to the field to cull the birds, but trumpeter swans are a protected species.
Panicky swan causes blackout
Farmers are trying to scare the swans away with noise from propane cannons, which Crawford said has been met with some success — but are still not especially effective.
"These [swans] don't know [the sound of] hunting. They don't know [to fear] hunters, sitting underneath them shooting at them with their shotguns, so these noises really don't do anything. They might spook them a little bit, but they'll come right back."
Meanwhile the cannons have caused their own problems. Recently a panicky swan got spooked and flew into a power line, causing a blackout at the home of a nearby non-farmer, who complained publicly about the outage.
Crawford said he's working with the Cowichan Valley Regional District to explain to non-farmers in the area that there is noise and other inconveniences associated with living in an agricultural area.
"You have moved to the farmland now. You're going to have noises, and farms farm 24 hours a day."
To hear the full interview with Bob Crawford, click the audio labelled: Farmers vs. trumpeter swans.