Tell them it is a dam and you will be fine.
http://www.fnzas.org.nz/fishroom/landsc ... 11825.html is the link to my pond building saga but you will be able to go even bigger, deeper and better.
Depth is good and you need it big enough so the bridge doesn't overwhelm it. Don't have something with pockets around the edges as this will give you dead water areas where algae etc will love to grow. Oval, square, rectangular or kidney are easy and good shapes. I don't think temperature is a problem where you are otherwise I would recommend at least 90cm depth.
One problem you may have is with ducks. They will pollute a fishpond, make a mess and eat the fish :roll: