Freshwater drainage systems, fed by melting of nearby inland ice and perennial snowdrifts, exist in the south-eastern part of arid, ice-free, coastal Vestfold Hills. Most important is the complex Druzhby system. Intriguing questions arise about the conditions controlling its seasonal development and about the consequences of possible changes of those conditions. A water-balance was calculated for 1990–91. The system went through four seasonal phases of which only one displayed a fully developed external drainage. Evidently, the relative duration of those phases can vary considerably from one year to another. The system depends critically on the water supply from ice-dammed Chelnok Lake, which could readily be drained by a minor retreat of Sørsdal Glacier. Exposed to excessive evaporation, the large Crooked Lake would then become internally drained and reach a new equilibrium in ∼830 years. A Crooked Lake sediment core can be interpreted as suggesting this occurred during the Holocene. The idea, inferred from striae, of a late Holocene Chelnok Glaciation reaching the northern shores of Crooked Lake is questioned. Instead, it is suggested that the Chelnok striae originate from local basal melting of the ice sheet draining southward into a deglaciated Sørsdal trough. At present, runoff is determined by opposing short and long-term climatic influences.