Sitka has two dams, both of which supply hydropower to the town and one of which also supplies drinking water. Both feed the water through long tunnels carved into the mountains, which are emptied once a year (at different times, of course) so maintinence personel can walk through and inspect them.
The main dam at Blue lake is closer to town and used to provide water and power to the large pulp mill nearby. This dam is unaccesible to normal people, but if you're agile enough you can climb around the gate and get to the long enclosed ladder leading down a cliff to the dam.
The other dam is at Green lake, several miles out a closed road which is accesible only by walking or biking. It is easier to mess around on, and you can climb down along the face of it with a series of ropes. At the bottom is the large outlet pipe leading into the side of a hill, and a nice reassuring leak spurting water out above the pipe. The area at the top of the dam has lots of scaffolding and metal stacked around, apparently to lower down the side of the dam and inspect it. At each of these dams is a battered aluminum boat whcih you can borrow if you bring your own motor. A log boom prevents boats from getting swept over the dam (but there's some nice big trees stuck in the overflow!)
The Green Lake dam
The dam outlet pipeline
Looking Up from the outlet pipe...
The end of the pipeline; the turbine building and the outflow gushing into the ocean. A sign which you have to be really close to read warns boats not to get too close...