Downstream from Black Bay, where the Spokane River leaves Coeur d'Alene Lake and splits around rocky islands nine miles from the lake, the river narrows into three channels, each with its own natural falls. Frederick Post saw the power in that drop first. His timber-crib dam on the north channel, about 20 feet high and several logs thick, diverted water to his sawmill. It had no head gates, so high water simply flowed over the top. When the mill burned in 1902, the little wooden dam survived the fire untouched.
Two years later Washington Water Power bought Post's site and set out to build something far larger: a dam across each of the three channels, with a brick powerhouse in the middle channel, the deepest and most confined of the three. The middle dam would form the powerhouse's upstream wall, while the dams on the north and south channels would handle spill in high water and hold the forebay steady in low water. It was an ambitious plan for a site that could only be worked with horses, manpower and ingenuity.
The builders started, fittingly, with Post's own work. His wooden dam was so well built that the crews reused it as a cofferdam while they raised the north channel dam, bolting its base to natural rock and to a substructure and filling it with concrete to make a watertight seal against the bedrock. Above the river they erected towers and a trolley system to deliver lumber for forms, carry concrete and lift head gates, so the middle-channel powerhouse could rise while spring runoff still passed freely through the north and south channels.
Electricity helped build the plant that would make electricity. Washington Water Power ran a 60-kilovolt transmission line from its Spokane plants to the construction site, giving crews steady power for rock crushers, concrete mixers, cableways and pumps instead of relying only on small engines and boilers. Winter brought its own problem, and its own answer: a steam boiler supplied hot water for mixing concrete, and steam was piped under tarps so the fresh concrete could set in freezing weather rather than wait for spring.
The pace held. The powerhouse went into service in July 1906, its first three generating units each rated at 2.25 megawatts, with a fourth added in 1907 and a fifth in 1908. A sixth unit, added in the 1980s, brought the plant to 14.75 megawatts. In all, the three dams and the powerhouse were completed in just two years, and the plant has served mines, mills, factories, railways, businesses and cities across northern Idaho and eastern Washington ever since.
That two-year build is getting a careful second act. Avista, Washington Water Power's successor, assessed the North Channel Dam in 2021 and began a spillway rehabilitation in spring 2024, scheduled to finish in spring 2027. Crews are replacing all nine spillway gates, their hoists, piers and abutments, repairing concrete and upgrading electrical and control systems, while most Falls Park trails stay open. For Black Bay neighbors who walk those overlooks, the work overhead is the same river craft, carried on more than a century later.
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