The Caspian is called a sea, but is really the world's largest lake. Iran, Russia, Azerbaijan, Kazakhstan and Turkmenistan sit around it.

It is also a working route for oil, gas and cargo.

Its level is going down.

Iran's environment officials put the fall at 20 centimeters a year, 2 to 2.5 meters in a decade, and the lowest in 200 years.

The reason is simple. Less water comes in from the rivers, and warmer water goes off into the air faster.

When the level drops, ships have trouble getting into port. Drop far enough, and the port stops working.

Yet the five countries are still talking not about the water, but how to divide the sea. A treaty in 2018 set out the shares, but in Iran the argument over ratifying it goes on.

The five are still arguing over their shares. The sea that those shares come from is getting smaller every year.