Early European colonists who settled along the Potomac found a diversity of large and small mammals living in the dense forests nearby.
Bison, elk, wolves ( gray and red) and panthers (cougars) were still present at that time, but had been hunted to extirpation by the middle of the 19th century.
 Among the denizens of the Potomac's banks, beavers and otters met a similar fate, while small populations of minks and martens survived into the 20th century in some secluded areas.

There is no record of early settlers having observed marine mammals in the Potomac, but several sightings of Atlantic Bottle-nosed Dolphins (Tursiops truncatus) were reported during the 19th century.
 In July 1844.
a pod of 14 adults and young was followed up the river by men in boats as high as the Aqueduct Bridge (approximately the same location occupied by Key Bridge today).

Since 2015, perhaps as a result of warmer temperatures, rising water levels in the Chesapeake Bay and improving water quality in the Potomac, unprecedented numbers of Atlantic Bottle-nosed Dolphins have been observed in the river.
 According to Dr Janet Mann of Georgetown University's Potomac-Chesapeake Dolphin Project, more than 500 individual members of the species have been identified in the Potomac during this period.
Early European colonists who settled along the Potomac found a diversity of large and small mammals living in the dense forests nearby. Bison, elk, wolves ( gray and red) and panthers (cougars) were still present at that time, but had been hunted to extirpation by the middle of the 19th century.  Among the denizens of the Potomac's banks, beavers and otters met a similar fate, while small populations of minks and martens survived into the 20th century in some secluded areas.
There is no record of early settlers having observed marine mammals in the Potomac, but several sightings of Atlantic Bottle-nosed Dolphins (Tursiops truncatus) were reported during the 19th century.  In July 1844. a pod of 14 adults and young was followed up the river by men in boats as high as the Aqueduct Bridge (approximately the same location occupied by Key Bridge today).
Since 2015, perhaps as a result of warmer temperatures, rising water levels in the Chesapeake Bay and improving water quality in the Potomac, unprecedented numbers of Atlantic Bottle-nosed Dolphins have been observed in the river.  According to Dr Janet Mann of Georgetown University's Potomac-Chesapeake Dolphin Project, more than 500 individual members of the species have been identified in the Potomac during this period.
Potomac River