This study assembles and analyzes published and unpublished data on inorganic nutrient concentrations in the waters of Kāne‘ohe Bay, O‘ahu, Hawai‘i, over the past 48 yr, but particularly over the 34-yr period since elimination of the major point-source of input of nutrients in 1977. As reported in a previous study, in the 1.5-yr period immediately following termination of the point-source input of nutrients (1978–1979), concentrations of PO₄^2- NO₃^- NO₂^-, and NH₄^- in the water column declined in all three basins of the bay, followed by improvement in the state of the benthos and planktonic communities. Since 1979, nutrient concentrations have remained low (PO₄^2- < 0.15 µM, NO₃^- NO₂^- < 0.30 µm, NH₄^- < 0.15 µM) despite continued growth of the human population in the bay's watershed. Increase in nutrient levels in the bay in the 1960s probably contributed to a phase shift from corals to the macroalga Dictyosphaeria cavernosa in the 1960s. Decline in nutrient concentrations beginning in 1977 may ultimately have contributed to the drastic decline in this alga that occurred in 2006. A protracted rainfall that occurred in spring 2006 produced elevated average nutrient concentrations for the year, but nutrient concentrations fell back to pre-2006 concentrations within 1 to 2 months. The record also contains evidence of a decrease of nutrient concentrations in the bay in response to a 4-yr period (1998–2001) of lower than normal rainfall. The response to elimination of the point-source input of nutrients and the responses to a season of exceptional rainfall and years of drought indicate that conditions in the bay's water column are dependent on both natural events in the bay's watershed and human activity. Kāne‘ohe Bay is one of a number of marine and aquatic systems whose degradation has been reversed by terminating nutrient addition caused by sewage disposal.