Like every morning, Sonia, who is retired and in her sixties (she did not wish to give her full name), was exercising on the pedestrian promenade of Aktaou, a port city of Kazakhstan, on the banks of the Caspian Sea. The receding shoreline? "Of course, everyone can see it," she exclaimed, pointing to the rocks and wild plants beneath the promenade. "The water used to come right up to here," dozens of meters from today's level.

Further along the coast, small shells still line the sand, well away from the first waves of salt water. They too are a sign that a few years ago the water was there, before it began to recede, without interruption since 2006. According to Kazakhstan's Institute of Hydrobiology and Ecology, the depth of this inland sea almost the size of Norway (371,000 square kilometers), located between Europe and Asia, is shrinking by 25 centimeters a year. In total, the depth of the Caspian Sea has fallen by two meters since 2000 and, in the space of 18 years, it is estimated to have shrunk by 22,000 square kilometers, half of which is in Kazakhstan.

For this Central Asian republic, the situation bears resemblance to the fate of the Aral Sea, between Kazakhstan and Uzbekistan, 90% of which dried up during the Soviet era.

Scientists are not as worried about the Caspian Sea, although the reasons for its decline are still debated. Some attribute this phenomenon to global warming and tectonic plate movements; others explain it by the fact that the sea "breathes," naturally alternating periods of regression and transgression. Between 1930 and 1977, the Caspian Sea retreated by almost 30 meters along the coast of Kazakhstan, before giving way to a period of sharp rise in water levels between 1978 and 1995. Some of the country's coastal towns were even partially flooded.

"Many remember this period of rising water levels, which is why few people are really concerned about the problem," said Kirill Osin, an environmentalist and activist. Contacted by Le Monde, the Ministry of Water Resources and Irrigation asserted that "there is currently no problem with the Caspian Sea drying up." "Of course, a drop in sea level will have negative consequences, which requires a study," the ministry added.

From the modest offices of his NGO Eco Mangystau, in Aktaou, Osin tries to warn of the dangerous decrease in the flow of rivers flowing into the Caspian, particularly the Volga, which is responsible for 80% of the freshwater inflow and whose flow is currently 212 cubic kilometers (km3), well below the norm of 238 cubic kilometers.

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