If the pH is extremely low or extremely high in a body of water, biological factors are largely affected: many animals can only tolerate a specific level. Natural factors that can affect pH levels include calcium carbonate in water, decomposition of tree matter, precipitation, photosynthesis and respiration, etc. Unnatural sources that can affect pH levels include acid rain (caused by air pollution), water pollution, mining (exposes rocks to rainwater which can produce acidic runoff). Additionally, pH can cause a bitter taste in water when at high levels and damage pipes when extreme