The Jadro River is a watercourse in Dalmatia, Croatia that discharges to the Adriatic Sea. The upper reaches of the Jadro River as well as its source are protected as an ichthyological nature reserve, partly due to the presence of an endemic species of soft-mouthed trout. The headwaters of the Jadro River were the original water supply for the ancient city comprised by Diocletian's Palace (now an area within the present day city of Split). Contemporary studies indicate favourable water quality levels of the river near the headwaters at Jadro Spring.