Suspended sediment concentration and transport processes are important controls on channel morphodynamics, hydraulic-engineering safety, and aquatic ecological and biogeochemical processes. Continuous monitoring supports flood regulation, reservoir operation, and navigation maintenance, and is also directly related to particulate carbon, nutrient, and contaminant transport, light attenuation, primary productivity, habitat quality, and the evolution of estuarine turbidity maxima. This framing expands SSC monitoring from a hydraulic measurement variable to a biogeoscience observation variable. This technical review uses a thematic literature search and synthesis to examine online and in situ monitoring methods for suspended sediment, including optical, acoustic, differential-pressure, vibration, electrical, nuclear, and sampling-based approaches. It compares their measurement mechanisms, applicable ranges, calibration needs, field deployment, and uncertainty sources. The review shows that sensor outputs cannot be directly equated with suspended sediment concentration. Site-specific conversion relations must be established by considering particle size, mineral composition, concentration range, hydrodynamic conditions, and paired sampling. Relations between turbidity, acoustic backscatter intensity, remote-sensing reflectance, and SSC are strongly site dependent, and nominal instrument accuracy cannot be directly converted into SSC accuracy. Future research should build a reproducible technical framework that integrates acoustic-optical retrieval, representative cross-sectional deployment, joint laboratory and field calibration, automated quality control, long-term drift correction, and uncertainty reporting.