The waters of Hamakua Canal once naturally flowed from Kawainui Marsh to the ocean. Located at the base of Puu O Ehu it joined with the waters of Kaelepulu Pond in Enchanted Lake. This stream was once throughly irrigated with small channels, and planted with taro patches. In the 1880s, Chinese rice farmers and Hawaiian taro farmers cultivated their crops in the shallow waters of Kawainui and Kaelepulu Ponds.

Hamakua Canal

The Hamakua anal was later dug deeper to help with flood control. The dirt that was dug formed a hill, called a berm, this eventually became the dike. When Kawainui Stream was deepened to become a manmade canal, they named it Hamakua Canal. This canal was totally closed off to Kawainui Marsh in 1987.

The water in the canal now comes from the street runoff, rain, and back wash from the ocean. Rain and ocean water changed the salinity of the Marsh water. Kawainui Marsh's salinity was recorded at 2 ppm (parts per million) in 1974. The water in Hamakua Canal was found to have 17 to 24 ppm in 1993. Student conducted tests in February 2002, showed results between 3 and 14 ppm. Some people consider this water too salty for use in Hamakua Marsh. Other contaminants may also be present. Further testing needs to be done. Another problem with the canal water, is the presence of talapia. These fish eat insects that birds feed on, as well as plants.