A interferometer-based fouling detection system and method are described. The system may include a fiber optic cable, a light source in communication with the fiber optic cable, at least one photo detector in communication with the fiber optic cable, and at least one interferometric spectrometer. The fiber optic cable may include a long period grating and a fiber Bragg grating or it may include a facet edge. The system may instead include a fiber optic cable, a light source in communication with the fiber optic cable, at least one photo detector in communication with the fiber optic cable, a fiber coupler, a reference probe including a mirror, a sample probe, and an interferometer.