Big Pond,
Good point, Terra Server is a great source. For smaller ponds, you may need to purchase the high resolution image. A GPS could be used to walk the shoreline and calculate the area. There is other mapping software like Terrain Navigator that can be used provided the pond is large enough to be mapped, or you can always sketch it in using the software. I have provided a link to the USFS wetland mapper, which is fairly new. Many of your ponds may be included on this database if your particular area is covered. Follow the sequence through to the mapper and then zero in on your area.
We use Terra Server images at work quite often and I have a couple framed in my basement of my favorite hunting and fishing spots. Personally, I still favor the county photo approach but its a matter of availability and preference.
USFS Wetland Mapper
