Total dissolved solids (TDS) indicate the amount of ions, including salts and metals, dissolved in a certain amount of water. Some dissolved ions in water are common, such as some CO 2 from respiration by organisms, or salts in saltwater. However, above certain levels, TDS can be detrimental to ecosystems. Anthropogenic sources of high TDS are common, and include agricultural/pesticide runoff, sewage discharge, or increased salinity from de-icing salts.
The implications of TDS can be extremely difficult to explore, as the measurement does not differentiate between the different ions dissolved in water. Some ions may be beneficial, like nutrients, while some may be deleterious, like metals. Each type of substance can have a different effect on the physiology of the organisms in the environment.
The best way to lower the TDS level of your local creeks or rivers is by prevention.