In 2006, Waipā Stream on the North Shore of Kaua‘i, Hawai‘i, was placed on the state's Clean Water Act Section 303(d) List of Impaired Waters after sediment and poor stream conditions damaged water quality and aquatic habitat. Dense stands of unmanaged hau bush had grown into part of the stream, trapping sediment and plant litter and making it difficult for native fish to move through the waterway, as per a report by the U.S EPA Hawaii Department of Health, Clean Water Branch.Years of restoration work have since brought measurable changes. Average turbidity in the freshwater portion of Waipā Stream fell by 62%, while native fish populations returned to levels two to four times higher than when the project began.TIL CreativesIn 2006, Hawai‘i listed Waipā Stream, after dense hau bush trapped sediment and blocked fish. Today, restoration cut average turbidity by 62% and restored native fish passage [AI Image]How did Waipā Stream become impaired?Waipā's problems were connected to changes across the watershed. Over roughly 200 years, deforestation, intensive agriculture, cattle ranching and forest fires altered the native landscape and allowed non-native grasses, shrubs and trees to spread.Those changes affected how the forest handled water. The invasive vegetation reduced the landscape's ability to absorb and retain water, increasing runoff and speeding up soil erosion.You Might Also Like:Feral pigs added another problem. Their rooting, soil compaction and wallowing damaged native forests and further worsened runoff and erosion.Sediment from the steep upper watershed could then travel toward the lower floodplains. Because the lower areas had slow-draining soils, water infiltration was limited. The result was sediment-laden runoff reaching the lower parts of the stream.Hau bush made matters worse by trapping sediment and plant litter inside the channel. The buildup damaged spawning habitat and created a major obstacle for native ‘o‘opu, or Hawaiian gobies, which need to move through this section of the stream at least twice during their life cycle.The water quality problems were serious enough that state standards for turbidity were exceeded, leading to the 2006 impairment listing.A total maximum daily load for total suspended solids, used as a surrogate for turbidity, was developed and approved in 2008. Informative TMDLs were also developed for enterococcus and nutrients, including ammonia and total phosphorus. A watershed management plan for the Hanalei Bay Watershed later provided a framework for improving and protecting water quality.TIL CreativesIn 2006, Hawai‘i listed Waipā Stream, after dense hau bush trapped sediment and blocked fish. Today, restoration cut average turbidity by 62% and restored native fish passage [AI Image]What changed during the restoration?The Waipā Foundation received CWA Section 319 funding in 2016 for the Waipā Stream Restoration Project. Rather than focusing on a single source of pollution, the project used management measures at different points throughout the watershed.By 2023, the Waipā Foundation had completed the project after carrying out a wide range of restoration and pollution-control measures.Hau bush was removed and three acres of stream and riparian areas were restored. At least 100 feral pigs were removed from the upper watershed. Best management practices were introduced to reduce turbid water associated with work in the lo‘i kalo, and a constructed wetland was installed to filter turbid water from the lo‘i.Several small upland erosion hotspots were revegetated, while 1,000 feet of fencing was installed to keep livestock away from waterways. Twelve cesspools were also replaced within Waipā and neighboring Waioli and Waikoko watersheds.Other measures included biodegradable erosion-control fabrics, native riparian plantings, drainage improvements, water bars and in-stream habitat enhancement and bank stabilization.The restoration also included community involvement. Education, outreach and public engagement brought together community members, volunteers and students, helping support the work while increasing awareness of the watershed's restoration.Did the restoration improve water quality and fish habitat?Monitoring before and after a major stream-flushing event in 2018 showed measurable improvements in Waipā Stream.One of the clearest changes was dissolved oxygen, which increased dramatically. Native fish populations also returned at levels two to four times those recorded when the project began.Most importantly for the stream's aquatic habitat, fish passage to important spawning areas was restored.Average turbidity dropped by 62%. That improvement was enough for the freshwater portion of Waipā Stream to be delisted for turbidity.The estuary also showed changes during the project period. Turbidity steadily declined, while fecal indicator bacteria levels fell. Average Enterococcus values at the mouth of Waipā Stream have dropped by more than 50% since 2005, while average values for Clostridium Perfringens, another fecal indicator organism, have fallen by more than 50% since 2013.Nutrient conditions also improved enough for the Waipā Stream Estuary to be delisted for nutrients. Total nitrogen and total phosphorus remained well below applicable water quality standards, despite slight increases during the project period, while nitrate and nitrite levels improved to below the water quality standard.The work did not remove every impairment. The freshwater portion of the stream remains listed for enterococcus, while the estuary remains listed for turbidity and enterococcus.That means restoration is not finished. More work is needed to reassess important pollutant sources and address the remaining water quality problems.Still, the changes already recorded show what a watershed-wide approach can accomplish. The project did not rely on one intervention. It combined stream restoration, erosion control, invasive species removal, livestock exclusion, wastewater improvements, wetland management, monitoring and community participation.The result was a measurable reduction in turbidity, better aquatic habitat and restored passage for native fish in a stream that had faced years of sediment and water-quality pressures.The continuing involvement of the Waipā Foundation and the local community also provides a basis for work to continue beyond the project's formal completion.FAQsWhy was Waipā Stream listed as impaired?High turbidity, sediment and habitat problems contributed to the listing.How much did turbidity fall?Average turbidity decreased by 62%.