Excessive anthropogenic nitrogen fixation alters the nitrogen cycle and increases nitrogen deposition, leading to nitrogen saturation, which leads to forest decline and nitrate leakage into stream waters. Kureha Hill in Toyama Prefecture, Japan, is considered to be in nitrogen saturation, since many streams have contained high concentrations of nitrate for more than 20 years. This study verified the latest status of nitrogen saturation by comparing the latest data with 20-year observational data. Results showed that the current nitrate concentration in stream water is lower than that observed 20 years ago. However, the C/N ratio of the soil between 12 and 18, indicates that nitrogen saturation could take place. In addition, the net nitrogen mineralization and net nitrification rate showed no significant change from the past data. Based on the nitrogen leakage to the stream water, Kureha Hill’s nitrogen saturation was found to be less intense; however, its potential to produce nitrate has been unchanged for 20 years.