Maui's Underwater Springs: Dye Traces Wastewater to Sea

For years, concerns existed about treated wastewater reaching the ocean near Lahaina, Maui. These suspicions were validated by a University of Hawaii tracer study, which confirmed a link between underground injection wells and submarine springs off Kahekili Beach. Researchers injected dye into wells in July 2011, detecting its presence in ocean seeps approximately half a mile away after 84 days, indicating an average travel time of over a year.

Analysis revealed that about 64% of the injected wastewater emerged through these springs. The water from these seeps was warmer, more acidic, and nutrient-rich, exhibiting characteristics of sewage effluent. This nutrient-laden discharge impacted the Kahekili reef ecosystem. Recent research in 2025 indicated that the reef receives eutrophic groundwater discharge, with over half linked to injected wastewater.

The findings from the Lahaina Groundwater Tracer Study were instrumental in a lawsuit filed by environmental groups against Maui County. The case, County of Maui v. Hawaii Wildlife Fund, reached the U.S. Supreme Court in 2020. The Court ruled that a Clean Water Act permit might be necessary for pollutants discharged through groundwater if they are functionally equivalent to direct discharge into navigable waters.