The last vestiges of the dam-building era continue. But the era of the dam removers is well under way, as communities try to improve river habitat, restore fish migrations, or remove hazardous dams that are crumbling or no longer serve a useful purpose (though dam removal can also have potentially adverse consequences, such as the release of toxic sediments, or reductions in species that had adapted to the dam environment). In 2008, about 60 dams were removed, according to the advocacy group American Rivers. That adds substantially to the more than 300 dams that have been removed since 1999, and about 790 dams removed in the last 100 years, according to the group's tally.