C-12 is one of 14 or so water control structures in the Herbert Hoover Dike that is technically a culvert. While a significant structure, like the locks and gates controlling water in or out of the lake through the dike, culverts are tunnels, not channels open to the sky. Like all 32 of the major control structures along the dike, they require constant maintenance. Nearly all of them are undergoing a complete rebuild or replacement, as part of the Army Corps’ Herbert Hoover Dike Rehabilitation Program. The program started in 2001, and should be completed in the mid-2020 decade, after costing more than one billion dollars.