Waimanalo Stream at Waimanalo

Gazing at Waimanalo Stream, one might not guess its troubled past. Waimanalo, meaning “potable water,” ironically once held a stream so polluted it was uninhabitable for native species. Waimanalo Stream, part of the Koʻolaupoko watersheds, flows through this beautiful area of Oʻahu. The area has a rural atmosphere. It’s home to nurseries, small farms, and horse boarding facilities. These, unfortunately, contributed to the stream’s decline. Studies from 1999-2000 revealed high levels of nutrients and sediments in Waimanalo Stream. This led to its inclusion on the 2004 Impaired Waters list under the Clean Water Act. The pollutants came from a mix of sources like farms, homes, and roads. From 2009-2021, restoration efforts took place, funded by the Clean Water Act and the Hawaii Department of Health. These projects, spanning three phases, focused on best management practices. Landowners partnered to reduce nutrient and sediment runoff into Waimanalo Stream above Kalanianaole Highway. One success story involved converting a bare waterway into a lined one. This change reduced erosion while still allowing vehicles to cross. Another project established vegetative barriers along property lines. These barriers filtered and slowed runoff. Cover crops like daikon radish and sunn hemp were planted to improve soil health and reduce erosion. Water sampling and surveys guided these efforts, pinpointing pollutant sources. Farmers even received financial support to implement these beneficial practices. Waimanalo Stream’s story is a testament to the impact of human activity and the power of restoration.