The Caspian Sea, wedged in between Europe and Asia, is the world's largest inland body of water.

It spans 371,000 square kilometres (143,000 sq miles), but has shrunk in recent decades due to hotter temperatures and agricultural use. It has also suffered from pollution due to oil and gas exploitation.

"If we do not take the necessary actions, the great Caspian Sea will turn into a puddle without fish, animals, plants and people," ruling party MP Sergei Ponomarev told the lower house of parliament in a plenary session.

"Companies are not only ignoring environmental regulations, but are also shifting financial responsibility to the state, contesting fines or offsetting them with other payments," he added, accusing some of extracting oil and gas in protected areas.

The number of Caspian seals has dropped from one million to one hundred thousand, while people living in lakeside regions have suffered a decrease in life expectancy and increase in cancer rates, Ponomarev said.

Water levels in the Caspian Sea have fallen by 1.85 metres (six feet) since 2005, losing 31,000 square kilometres in volume, according to the "Save the Caspian Sea" advocacy group.

Kazakh President Kassym-Jomart Tokayev warned last year that the Caspian was "on the verge of extinction."

The sea borders five countries -- Azerbaijan, Iran, Kazakhstan, Russia and Turkmenistan -- and while all have become more aware of the problems affecting its fragile ecosystem, addressing them has been slow.

Russian President Vladimir Putin in December warned the Caspian must not "under any circumstances" be allowed to become another Aral Sea -- a lake further east which was once the world's fourth largest before Soviet irrigation projects dried most of it up.

The drop in the level of the Caspian Sea also has economic consequences, threatening the functioning of oil, gas and port infrastructures, and jeopardising ambitious transportation projects linking Europe and Asia.