I'm not sure exactly what you mean by the term weed but if the pond is becoming choked up with blanket-weed, the fine green shapeless mass or to be correct, 'fillamentus algae' Then its best to remove this til the owner gets back, you can reduce this by netting, raking, pulling or twirling it round a stick, some use an old lavatory brush.
Leave the weed up on the edge of the pond to allow any small creachers a chance to escape back into the water, a couple of hours or so should do it.
If its any other kind of weed ie an oxygenator or water lily etc, I'd just keep a small area clear for now until you hear from the owner.