The Collaborative International Dictionary of English v.0.48:

Brackish \Brack"ish\, a. [See Brack salt water.]
   Saltish, or salt in a moderate degree, as water in saline
   soil.
   [1913 Webster]

         Springs in deserts found seem sweet, all brackish
         though they be.                          --Byron.
   [1913 Webster]

WordNet (r) 3.0 (2006):

brackish
    adj 1: distasteful and unpleasant; spoiled by mixture; "a thin
           brackish gruel"
    2: slightly salty (especially from containing a mixture of
       seawater and fresh water); "a brackish lagoon"; "the briny
       deep" [syn: brackish, briny]

Moby Thesaurus II by Grady Ward, 1.0:

37 Moby Thesaurus words for "brackish":
   bad, barfy, briny, cloying, fetid, foul, fulsome, high, icky,
   maggoty, mawkish, nasty, nauseant, nauseating, nauseous, noisome,
   noxious, offensive, overripe, pickled, poisonous, rancid, rank,
   rebarbative, rotten, saline, salt, salted, saltish, salty,
   sickening, spoiled, stinking, vile, vomity, weevily, yucky