Since the water in a pond does not circulate too much, it would be best for you to spread the lime across the pond. One common way is to load it onto a flat pontoon boat (with sides removed) and use a gas operated pump to pump water and wash it off the boat while driving around the ond.
A cheaper, much harder method is to walk around the periphery of the pond tossing bucketfulls of lime onto the surface. It won't get the middle to well, but if it is a two acre pond and you get all sides. It will spread pretty good.
Im sure that there are some dudes on this site that have the equipment to spread it for you.
