The Kasplya (Belarusian and Russian: Каспля) is a river in Smolensky, Demidovsky, and Rudnyansky Districts of Smolensk Oblast of Russia and in Vitebsk Region of northern Belarus.

[1] It joins the Daugava in the urban-type settlement of Surazh.

The town of Demidov is situated on the Kasplya.

It flows north, crosses the border with Demidovsky District and turns northwest.

It flows through Demidov, and next to the selo of Boroda turns west, crosses Rudnyansky District and enters Belarus.