across major tectonic structures over a distance of 13–16 km as the crow flies (Figure 1). The tracer from Kujbyshevskaja Cave was also detected in a borehole located between these two springs, which yields groundwater from a depth of below sea level. This has been interpreted as an indication of the connection of the cave with the submarine discharge. The large "Central Karst Hydrologic System", which encompasses most of the southeastern flank of the Arabika anticline, had been identified in this way. The system became the deepest in the world with its overall vertical range of about (measuring to the borehole water-bearing horizon) or even (measuring to the deepest reported submarine discharge points). Another tracer was injected in the Moskovskaja Cave (−970 m) and detected at the Gegsky Vodopad spring, indicating the presence of a karst hydrologic system comprising the northeastern flank of the Arabika anticline (the "Northern System"). No connections have been revealed with yet another major spring, Goluboje Ozero in the Bzyb River canyon, although it apparently drains a large area of the eastern sector of the massif (the hypothetical "Eastern Karst Hydrological System"). It is not clear where Sarma Cave (−1,550 m) drains to, Goluboje Ozero to the southeast or Reprua to the southwest, at the shore. The results of the dye-tracing tests demonstrated that groundwater flow is not subordinate to the fold structure but is largely controlled by faults that cut across the strike of major folds, and that the large part of the central sector of Arabika is hydraulically connected to the springs along the seashore and with submarine discharge points. Krubera Cave has an extremely steep profile and reveals a huge thickness of the vadose zone. The lower boundary of the vadose zone (the top of the phreatic zone) is at an elevation of about at low flow, which suggests a low overall hydraulic gradient of 0.007-0.008. Low-TDS groundwater is tapped by boreholes in the shore area at depths of 40–280, 500, 1,750, and 2,250 m below sea level, which suggests the existence of a deep flow system with vigorous flow. Submarine discharge along the Arabika coast is reported at depths up to ~400 m b.s.l. It is difficult to interpret these facts in terms of the development of karst systems controlled by contemporary sea level, or within the range of its Pleistocene fluctuations (up to −150 m). In combination with the existence of