Acid rain is rain or any other form of precipitation which is unusually acidic. It has dangerous effects on the environment and on structures. It is mostly caused by emissions due to human activity of sulfur and nitrogen compounds which respond in the atmosphere to produce acids. In recent years, many governments have introduced laws to lessen these emissions. Both lower pH and higher aluminum concentration in the surface water that occur as a result of acid rain can cause damage to fish and other aquatic animals. At pHs lower than 5 most of the fish eggs would not hatch and lower pHs can kill adult fish. As lakes become more acidic biodiversity is also reduced. Soil biology can be critically damaged by acid rain. Some tropical microbes can quickly consume acids but other microbes are incapable to tolerate low pHs and are killed. The enzymes of these microbes are denatured by the acid. The hydronium ions of acid rain also mobilize toxins and filter away essential nutrients and minerals