Acid rain is caused by emissions of sulfur dioxide and nitrogen oxides from the burning of fossil fuels which react with water and oxygen in the air to form acids. When acid rain reaches the earth, it flows across the surface and soils, entering water systems and making waters acidic. Acid rain harms aquatic environments by making waters toxic and absorbing aluminum from soils. It also damages forests by depleting nutrients from soils and releasing aluminum, harming trees' ability to absorb water and reproduce. Reducing emissions from fossil fuels and promoting alternative energy sources can help lessen acid rain.