(gentle music) (sea wave bubbling) >>In the Sargasso sea, microscopic larvae invisible to the naked eye hatch in droves and drift in the ocean waters for about a year.

(ocean water bubbling) Eventually, the currents propel them to the American East Coast.

As they approach the shoreline, the faintest presence of fresh water prompts these larvae to transform into transparent noodle-like creatures, and develop fins.

(bright gentle music) Rushing inland, the surge of fresh water sparks the development of pigment, providing essential camouflage from predators.

Over the course of another year, they double in size as the freshwater environment transforms their bodies.

Lulled by the call of home, the determined creatures swim upstream as high as 3,000 feet above sea level.

(river water sizzling) At last, in the upper regions of the Rapidan River, they transform into long snake-like creatures.

This is the American eel.

As the only freshwater eel species native to North America, they hunt in these rivers for up to 40 years, (river water bubbling) but one thing they won't do up here is reproduce because they are neither male nor female.

Only as the years go by, after growing two to three feet long, does this one even develop a sex.

(river water sizzling) At this stage, her eyes enlarge by 10 times, her fins broaden, and her skin color changes yet again to silver.

This metamorphosis prepares her for her final journey.

(river water sizzling) What drives her remains unknown, but she instinctively travels back down river to the Atlantic to the exact place where she was born.

(gentle music) How she knows where to go continues to be a mystery, but once there, she congregates with other eels hundreds of feet deep in the water where they spawn.

The eels' journey ends here where they die after mating, ending a life cycle that can last almost half a century, (ocean wave bubbling) but as their eggs hatch, the circle of life sparks the next generation of eels to rise again back home to the mountain streams of Shenandoah.

(soft wind blowing) (bright music)