The Instruch (Russian: Инструч; German: Inster; Lithuanian: Įsrutis, Įsra; Polish: Wystruć) is a river in Russia's Kaliningrad Oblast. It begins northeast of Dobrovolsk and, along with the river Angrapa, forms the Pregolya near Chernyakhovsk.

Prior to 1945, the river was part of German East Prussia. The town of Insterburg (now Chernyakhovsk) was named after the river's German name, Inster.