For some months a resident in Riverside Walk has hosted at the bottom of their garden a water quality probe for Plymouth River Keepers.
The monthly results are here: https://tinyurl.com/3mhuphp7
The probe takes a reading every 15 minutes on depth, temperature and conductivity. In particular, it is conductivity that of interest. Conductivity is a measure of the total dissolved solids within a watercourse. In the Tamerton Foliot catchment there is low natural dissolved solids, so as a general rule an increase in conductivity is likely to be human-related. An increase in conductivity could be due to a number of factors such as sewage entering the river, industrial or chemical discharge or farm run-off.