Wetlands Conservation Investment Act of 2011 - Amends the Internal Revenue Code to treat gain or loss from the sale or exchange of a mitigation bank credit by the sponsor of the mitigation bank (i.e., the wetland, stream, or other aquatic resource area that has been restored, established, enhanced, or preserved for the purpose of providing compensation for unavoidable impacts to aquatic resources) who earned such credit as the sale or exchange of a capital asset held for more than one year (thus allowing preferential tax treatment of such gain or loss). Exempts from tax withholding requirements any gain from sales of mitigation bank credits.