Is my river birch dying or just stressed?

The signature problem here is iron chlorosis — leaves turn chartreuse or yellow with darker green veins, worst on new growth at the top — because river birch wants acid soil and central Indiana's glacial clay typically runs neutral to alkaline. Stress is normal summer leaf drop in a dry August, which a mature river birch does routinely and recovers from; dying is thin, sparse crowns with dead twiggy tips at the top over consecutive seasons and chlorosis that deepens each year, since twig and branch dieback is chronic in this species and the dead parts shed readily.