The productivity of the sea is influenced by water temperature, salinity and nutrient content. The organic matter and phosphorous and nitrogen (nutrients) of the sea derives almost exclusively from its tributaries, which carry domestic, industrial and agricultural effluents. Organic matter and nutrients either provides the food for the basic organisms (plankton, zooplankton and zoobenthos) or degrades. Degradation of organic compounds consumes oxygen, reducing the oxygen content of the water.

Oxygen depletion in the bottom water causes the death of bottom-living animals, which are often the food for higher organisms and part of the fish food-chain. More widespread oxygen deficiency may also directly cause fish mortality. Greatly depleted oxygen levels result in almost complete removal of the higher orders of life (fish) from the sea, and would thus be commercially disastrous.

Nutrient levels have fallen since the break-up of the Soviet Union and the resultant reduced economic activity. They appear to have stabilized at a lower level and the effects diminished. Provided the influx of nutrients does not increase again, it is assumed that the risk of damage from eutrophication will not be serious. Likewise, provided new sewerage schemes include the appropriate effluent treatment works, regenerated industry adopts modern waste standards, and agricultural discharges are controlled, there should be a reduced risk from eutrophication of the sea.

Hydrocarbon products enter the Caspian Sea naturally from the erosion of rocks and emissions from sea-bed mud volcanoes. Coastal oil production facilities that have been flooded by the recent rise in sea level attract considerable interest. In terms of overall pollution of the sea, they are of minor significance only but may be locally significant.