WISCONSIN DELLS — Decades before the construction of Wisconsin’s first coal-fired generator, an engineer named Magnus Swenson and his partners harnessed the power of the Wisconsin River behind a wall of concrete.

More than a century later, the Kilbourn dam is still churning out electricity, enough to power nearly 5,000 Wisconsin homes last year, one of more than 140 hydroelectric dams that generated more than 4% of Wisconsin’s electricity supply last year — and nearly half of all renewable energy.