Duck pond = serene, idyllic, pleasant
Dog pound = sad, tragic, pathetic

Despite the major differences in connotation pond is actually an alteration of pound. Both words are from the Old English pund meaning "enclosure". Pund is also the first element in the Old English compound pundfald (fald being the root for our Modern English fold, as for sheep), which gives us our Modern English pinfold (aka penfold). And, interestingly, even though pinfold/penfold is an enclosure for animals pen (in the enclosure sense) comes from a completely different Old English root.

Beyond Old English the origins of pound (in the above sense) are unknown; there are apparently no cognates in other languages. Check out WWW for more on pound's exciting history.

pond [OED]
pond [AHD]
pond [Online Etymology Dictionary]

Labels: Old English, The Daily Hump