Mitigation bank means a site where wetlands and/or other aquatic resources or natural habitats are restored, created, enhanced, or in exceptional circumstances, preserved, expressly for the purpose of providing compensatory mitigation in advance of authorized impacts to similar resources. For purposes of the Clean Water Act, Section 404 (33 U.S.C. 1344), use of a mitigation bank can only be authorized when impacts are unavoidable.
23 CFR § 777.2
In addition to those contained in 23 U.S.C. 101, the following definitions shall apply as used in this part: