Cooling water discharge
In coal power plants with once-through cooling systems, once the 70 to 180 billion gallons of water have cycled through the power plant , they are released back into the lake, river, or ocean. This water is hotter than the water that receives it, creating "thermal pollution" that can decrease fertility and increase heart rates in fish.
Typically, coal power plants also add chlorine or other toxic chemicals to their cooling water to decrease algae growth. These chemicals are also discharged back into the environment.