You asked this yesterday, too, so I did a bit of research for you, using my town, Juneau, Alaska as an example.

Starting in 1880, Juneau was the site of massive industrial-scale gold mining and refining. Huge stamping plants were built on Douglas Island, just offshore of mainland Alaska, and other mining operations on the mainland demanded huge amounts of electricity as well.

Initially, the Treadwell Mine works on Douglas Island used direct waterpower. Diversion projects were built to bring water to places where water wheels could drive machinery or supply steam plants. The first electrical power plants were developed in the last years of the 19th century.

In April 1913, work began on the Salmon Creek Dam on the mainland, across Gastineau Channel from Douglas Island. When completed, it was the world's first constant-angle arch variable radius dam. At 168 feet high and 648 feet across at its crest, the design used 20 percent less concrete than a standard arch dam built at the time.

Two powerhouses were built to handle the flow from the dam, and together they had an installed capacity of 6.7 MW. While the powerhouses have since been replaced, the dam still operates today.

There's lots of other interesting dams in the Juneau area, but I want to mention a different project, the Annex Creek power project. This involved tapping Annex Creek Lake, a natural reservoir about 800 feet above sea level. Engineers drilled a tunnel to tap the lake at a depth of 150 feet, creating a usable power reservoir without the need for a dam.

The Jan. 15, 1916 issue of The Engineering and Mining Journal states that "the first unit will develop 4,000 hp., and it is planned to double this power with the second unit, to be installed later."

You asked for MW, and the same journal states that Salmon Creek generates "8,000 hp." so I would venture to say that Annex Creek had an installed capacity similar to Salmon Creek.