It begins in a narrow, high-walled valley [2] in the central mountains and enters the Pacific Ocean on the northwestern coast of the island, just east of Wainiha, on the western edge of Lumaha'i Beach.

The river debouches into the Pacific Ocean on the northwestern coast of the island, just east of Wainiha, on the western edge of Lumaha'i Beach.

[8] Measuring 4,000 feet (1,200 m) in length, the beach has rocky features at the mouth of the Lumaha'i River, which results in treacherous "rip currents".

[10] A black lava formation abuts the west bank near the mouth which is named Ke-alelo-O-Pilikua, meaning "tongue of Pilikua".

[5] In the hills of the river valley there is a rock formation known to the Hawaiians as Ma’ina-kehau, which is a very large boulder resembling a man with a "grey body and white head".

[4] The Lumaha'i river valley once witnessed toro and rice farming by the immigrant farmers from other regions of Hawaii, China and Japan, between 1890 and 1930.