The irrigation of lowland river valleys has decreased the fresh water flowing into the caspian sea which in turn has caused a reduction in__

d. Fish

Explanation:

The Caspian Sea is between Europe and Asia, its resources are disputed by five different countries; Azerbaijan, Kazakhstan, Turkmenistan, Russia, and Iran. Among the disputed resources is fish.

The Caspian Sea is rich in sturgeon, fish from which caviar is obtained, but every year freshwater dismonition has unbalanced the ecosystem, as well as overfishing, leading to sturgeon becoming increasingly scarce.

I hope this information can help you.

your answer is b hope that