US Wetland Mitigation Banking — CWA Section 404 Compensatory Mitigation

Under Clean Water Act (CWA) Section 404, developers and agencies whose projects unavoidably impact 'waters of the United States' must first avoid and minimise harm; remaining losses require compensatory mitigation equivalent to or greater than the ecological loss. Since federal guidance was issued in November 1995, mitigation banking — purchasing pre-verified credits from a third-party bank that has already restored, created, or enhanced wetlands — has become the preferred compensatory mechanism.

The US Army Corps of Engineers (USACE) and EPA jointly oversee the programme through the RIBITS tracking system. The Transportation Equity Act (1998) designated banking as the preferred alternative for federally funded transport projects, and the 2008 Compensatory Mitigation Rule established equivalent performance standards across banking, in-lieu fee programmes, and permittee-responsible mitigation.

By 2013, over 1,800 bank sites were registered — up from 46 in 1992 — of which 62% are privately operated. The 219 banks approved by 2001 encompassed approximately 139,000 acres, and credit prices range from a few hundred to over US$100,000 per credit depending on location and resource type.

Evidence of ecological effectiveness is nuanced: the 2001 National Research Council review found that mitigation sites reliably generate wetland acreage but documented inconsistent functional equivalence and long-term monitoring gaps at individual sites, and subsequent studies found outcomes vary markedly by geography, ecosystem type, and bank sponsor.