The necessity to study the oxygen activity of aqueous media in the flowing state to solve various problems has been substantiated. It has been found that emitted γ-quanta as a result of decay of 16N nuclei with energy more than 9 MeV cause the formation of additional color centers and reversible optical defects in the fiber. Their appearance leads to increased radiation-induced losses in the optical fiber, which reduce the power of laser radiation transmitted through it. A new optical method has been developed that makes it possible to study the nature of oxygen activity change by the number of γ-quanta emitted by 16N nuclei when the liquid moves along the pipeline. For the first time, the nature of the change in the spectral distribution of the number of 16N nuclei emitted as a result of oxygen activity was investigated, and its features in the current flow were determined. In order to realize long-term studies of oxygen activity, a method was proposed to restore optical properties of fiber in the presence of background radioactive radiation. Keywords: