At the same time, fewer dams being built and the removal of older dams allows the groundwater to reach the ocean more quickly. (insteading.com)
They add that their findings support the practice of leaving old dams in place in Europe and North America where beavers — whose numbers have plummeted over the last 150 years — are making a comeback. (sciencemag.org)
Surprisingly, it doesn't occur when beavers move back into old dams: Methylmercury levels above and below recolonized dams were nearly identical in the study. (sciencemag.org)