The Environmental Protection Agency (EPA) exempted incidental vessel discharges in U.S. waters for more than 30 years under the Clean Water Act until 2009. A 2008 federal circuit court of appeals decision (Northwest Environmental Advocates v. EPA) invalidated that exemption and required EPA to issue vessel discharge permits. EPA responded with a general permit effective December 19, 2008. A key issue for the industry was the ability of states to supplement the general permit with local requirements creating a potential patch work of environmental requirements. The Lake Carriers' Association, Canadian Shipowners Association and American Waterways Operators challenged the general permit in court.  They claimed, among other things, that an inadequate opportunity to comment was provided on the various state standards which they further claimed EPA had the authority to adjust. On July 22, 2011, the District of Columbia federal circuit court of appeals rejected the challenge determining that the petitioners' waived their argument regarding EPA's authority by failing to raise it in comments submitted to the agency.