bigolbug:
at least 100ft with obstructions such as water.
You should put some thought into what, exactly, the requirements are here. It will matter a lot.
30 m of water -- eg: transmitting from under a lake -- is simply not feasible for any sort of radio you can easily obtain, be it bluetooth, Xbee, 802.11, 433Mhz, 315Mhz, 900Mhz -- all of them will fail.
If the obstructions will be rainy weather, trees and maybe buildings, you may find that the 433Mhz jobbers give you the range you need. At $10 per pair, your best bet is to get some and experiment.
You do not mention how much bandwidth you need -- how many messages/sec or bytes per minute do you need? and any latency requirements you may have. These will tend to narrow the field as to what will or won't be feasible.