Lemond33 ,
a deer gets quite a bit of it' s water needs from the food it eats , and they will drink from whatever water is available if it' s close . I' ve seen them drink from small seeps , puddles on tree stumps , creeks , horse troughs etc. Brackish water is probably not to their liking if fresh water is available , even from a small unreliable source . They don' t neccessarily tear up the ground while drinking like they do mineral licks , are there tracks around the water hole ? . Your brackish swamp may also have fresh water sources that you' re not aware of , look for tiny fresh water spring outlets . Better yet , concentrate on finding their bedding areas .