The surface waters of Morristown National Historical Park support a diverse and balanced fish community. As part of the National Park Service Inventory and Monitoring Program, a fish inventory was conducted in 1999.
Eleven fish species were documented, eight of which were native while the remainder were introduced. The most common species were Slimy Sculpin, Blacknose Dace and Tesselated Darter.
The State of New Jersey has listed the sections of two waterways that flow through the park as "Wild Trout Streams". The wild trout stream designation serves to identify stream segments with viable wild trout populations capable of supporting a limited sport fishery.
The designation also provides an additional level of protection to these wild trout populations by eliminating fish stocking activities and establishing more stringent fishing regulations.
Both Indian Grave Brook and the Passiac River support viable populations of Brown and Rainbow Trout. The Passiac River also contains Brook Trout.