[en] Several types of submerged Si detectors with the sensitive surface from 1 to 1000 mm² have been developed for determining remotedly specific alpha-activity of conductive aqueous solutions without preparation of dry specimens. The sensitive surface of the detectors is in a direct contact with a solution under investigation. Designs and operation parameters of several alpha detectors which are based on both n-and p-type Si are described. The measuring procedure is also described. The specific alpha activity of a solution is shown to be directly correlated to the counting rate of a detector, alpha particle energy, solution density and mean atomic number of solution constituents. The problems of matching parameters of the detectors and pulse amplifiers, radiation resource of the detectors and the effect of a β-radiation large background are also discussed. The submerged detectors allow to measure alpha-activity with accuracy of 5-20%