[dghughes]

My province does it's mainly for the fish. It is called a buffer zone I'm not sure of the dimensions. The province even buys up land from old farms that have fields that used to go right to the water edge.

Even the orientation of furrows helps. Not having them perpendicular to the river the furrows should be parallel.

Even provincial workers cutting trees need to use canola oil for bar oil (bar and the saw chain lubrication).

Farms can have runoff of fertilizer and it can cause fish to die rapidly in large groups aka a "fishkill". The farmer is fined too.