The Federal Water Pollution Control Acts have been attempts to legislate reductions in water pollution in the United States. There are two main forms of control of water pollution, source reduction and other forms of mitigation.
Source reduction means reducing the amount of contaminants released into the water. This might include wastewater treatment plants, regulation of what industry and agriculture can release into groundwater, placing heated wastewater into holding tanks to cool off before returning it to rivers, having ships empty waste into tanks in harbors to be treated rather than into the ocean, etc.
Mitigation involves reducing the harm of contaminants that have been released into the environment by such tactics as wetlands restoration or using various techniques such as physical barriers or chemical dispersants to clean up oil spills.
Love Canal, Deepwater Horizon, and Exxon Valdez are specific cases where these techniques have been put into practice.