From the 1960s onwards, there were gradual but steady improvements to the inadequate sewage works and sewers built during the Victorian era in the urban areas, but this was expensive, and took time to complete. The changes were helped by the introduction of more stringent pollution control legislation, which required industrial waste to be discharged to sewers, and the formation of the Trent River Authority, which had new duties relating to managing water quality issues. Other changes, such as the replacement of town gas with natural gas, saw the end of the polluting and toxic coal tar emissions to rivers in 1963.