Description: With the increasing aging of an upwelling body of water, a pronounced rise in the saprophyte counts was found at first in the surface water and later also in the deeper zones. They increased, for example, at a depth of 15 meters, from 30-50 to 250 bacteria/ml, which represents a production of 4 X 10-3 mg bacterial C/m3 water. Different bacteria populations were included on the medium used for isolation, which was prepared with both sea-water and fresh water. On the former, which had relatively few species represented, the spectrum ranged from whitish to yellowish-white halophilic marine bacteria. On the tap water medium, however, dominated a spectrum of white or vividly pigmented bacteria, comprising many species, with maximal development in fresh water. It is supposed that bacteria of terrestrial origin are involved here, which are possibly carried to the sea by sand or dust storms. With regard to the colony forms, no difference between the bacteria populations within or without the upwelling water could be determined. The greatest bacterial infiltration of the sediment was found on the surface (between 16 X 103 and 80 X 103 bacteria/cm3). Already in the upper 2 cm, a strong reduction of the saprophyte count was determined, together with a relative increase of those bacteria which possess a greater range of ecological amplitude. The saprophyte counts on the sediment surface decreased with an increase of water depth. On 21 strains of bacteria isolated from the open waters, investigations were carried out on their morphological characteristics and the most important metabolic reactions.