The paper reports on contributions and limitations towards the long-term deployment of in-water sensors, on commercial tidal stream turbines, for monitoring of turbine condition and performance. It is recognised that specific site and ever time varying flow conditions pose monitoring challenges. For all turbine and/or blade deteriorations, fault diagnosis and prognostics are vital elements to secure planned maintenance operations. Approaches and results are reported from within the wider Cardiff Marine Energy Research Group (CMERG) activities. In particular results from 2 different experimental regimes are reported; water flume testing of a 0.5m diameter physical scale model; and wind tunnel evaluations using smaller scale models, of blade and support structure constituents. The application field is reviewed, along with introductions, justifications and discussion of the approaches used.