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Wailuku River on the Big Island

Posted: April 24, 2008

I hiked in the Hilo Forest Reserve along the middle reaches of Wailuku River on the Big Island to explore and photograph the native plants and animals that live along the river. 

Wailuku River starts out as a trickle at the 10,800 foot level of Mauna Kea and increases substantially in volume as drains the Hilo watershed over its 26-mile descent to the sea.  At the mouth of Wailuku River where it empties into Hilo Bay, the water volume averages an impressive 275 cubic feet per second making it the largest as well as longest river in the Hawaiian Islands. 

The hike to the middle reaches of Wailuku River started near the 15 mile marker on the Saddle Road where I made my way along a jeep road through native forests.  When I reached the 50-foot wide river bed scoured from lava rock I was at a point about halfway up the 26-mile river. 

The water was crystal clear with green filamentous algae growing on rocks submerged in the stream. As I made my way upstream to explore the river, each bend in the waterway brought a new surprise. 

One of the more unexpected sights were many koa trees along side the river.  Large koa branches arched gracefully over charming mountain pools along the stream. 

Koa and ohia trees, some decked with red lehua flowers, dominated the river banks.  The river cuts through extensive native forests as it makes its way downstream.  Unfortunately, the stream carries the seeds of invasive species from pasture lands upriver and distributes them downstream.  Gorse, strawberry guava, and other invasive plants are transported down the entire course of the river. 

There were a number of waterfalls and pools as I made my way upstream.  Unfortunately, I did not see native opae (shrimps) or oopu (fishes) in the mountain pools.  Instead I saw tadpoles, frogs, koi (carp), and other introduced species which were presumably released by people downstream in Hilo and made their way upriver. 

Much to my surprise, I saw a number of native damselflies (Megalagrion spp.) engaged in courtship rituals along the river.  These vibrant red damselfies are endemic to the Hawaiian Islands.   

The middle reaches of Wailuku River are an awesome place to visit.  Each twist of the river as it meanders over the landscape offers an endless variety of sights – charming waterfalls, quaint mountain pools, big old trees with gnarled branches, etc.  What a great place to explore. 

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National Park Service – Rivers and Trails – Hawaii Segment