The term 'Russian Sea' is often used to refer to the ARAL Sea, which is a large lake located between Kazakhstan and Uzbekistan. The ARAL Sea was once one of the four largest lakes in the world, but due to human activities such as over-irrigation and the diversion of rivers, it has been shrinking since the 1960s. As a result, the ARAL Sea has become much smaller and saltier than it once was, leading to environmental and economic problems in the region.