Alterations to pH levels can have significant impacts on species living in freshwaters. If the pH falls too low (increasing acidity) or gets too high (increasing alkalinity), organisms can die or experience sublethal effects. For example, when pH drops and the water becomes too acid, organisms with exoskeletons (e.g. crustaceans such as crayfish) can start "dissolving". This has dire effects on their recruitment, growth, and survival. Currently, acidification is a critical issue for freshwaters for many groups of organisms. Large changes to the species present in these acidified freshwaters can notably alter food webs and their subsequent functioning. Acidification is largely caused by chemical pollution from industry and transport. 

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Total Dissolved Solids (TDS) is a measure of the total inorganic and organic substances present in water. TDS can be used to gauge stream/lake/river quality. Common sources for TDS are agricultural run-off, urban run-off, leaching of soil contamination, point source water pollution discharge from sewage treatment plants, and clay-rich mountain waters. High amounts of TDS can affect the aesthetic quality of the water (i.e. does it look good to drink?) but can also have health effects if the TDS are pesticides. While direct toxicity of elevated levels of TDS to freshwater organisms is highly dependent on the particular chemicals in the water, it is possible for TDS levels to become high enough to e.g. reduce fertility or increase mortality. The effects of elevated levels of TDS can increase when other stressors are present, including high turbidity, abnormal pH, or reduced levels of dissolved oxygen.