The Hudson River in New York was contaminated with polychlorinated biphenyls (PCBs), a group of toxic chemicals, mainly released by General Electric (GE) factories from the 1940s to the 1970s. The river was cleaned through a combination of measures, including:

Source control: GE was held responsible for the contamination and was required to reduce the amount of PCBs entering the river from its factories. GE spent over $1 billion to remove the PCBs from its manufacturing sites and to improve its wastewater treatment systems.

Dredging: The most contaminated sediments were dredged from a 40-mile stretch of the river between Hudson Falls and Troy. Dredging involved removing sediment from the river bottom using large machines and then processing the sediment to remove the PCBs. Over 2.75 million cubic yards of sediment were removed over a six-year period.

Habitat restoration: After the dredging was completed, the river bottom was restored to a more natural state to provide habitat for fish and other aquatic life. This included placing large rocks and boulders on the river bottom to create a more diverse habitat.

Monitoring: The effectiveness of the cleanup was monitored through ongoing sampling and analysis of sediment, water, fish, and other wildlife in the river. The monitoring indicated that the PCB levels had decreased and that the river was becoming healthier.

The Hudson River cleanup was a complex and expensive process that took several years to complete. While there are still areas of the river that remain contaminated, the overall health of the river has improved, and it is now safe for recreational activities such as swimming and fishing.