Straight out of the Traffic Safety Act
Mudguards
64(1) A motor vehicle or trailer must have a part of its body, a fender or a mudguard that covers the width of each tire.
(2) The body part, fender or mudguard referred to in subsection (1) must be above each wheel and
(a) extend downwards at the rear of each axle or axle group to at least the centre line of the axle, or
(b) be a distance away from the ground equivalent to at least 1/3 of the horizontal distance from the bottom edge of the mudguard to the centre line of the axle, but not closer to the ground than 150 millimetres when the vehicle is loaded.
(3) In addition to the requirements of subsection (1), the following types of vehicle must be equipped with rear wheel splash and stone?throw protection that complies with SAE Standard J682:
(a) a commercial vehicle or combination of commercial vehicles that is registered for a gross weight of more than, or that weighs more than, 4500 kilograms and that is not a bus;
(b) a bus;
(c) a trailer.
(4) A passenger car is not required to have a mudguard.
(5) This section does not apply to a trailer designed and constructed for drive?on and drive?off low loads.