By midsummer, the reservoirs at the top of the Columbia River hydrosystem in Canada are full. From now until early spring 2015, this stored water, governed by the Columbia River Treaty, will increase and enhance the ability to generate reliable electricity for the entire Pacific Northwest.

Downstream at Wanapum Dam, things are still looking dry. A worrisome crack in the dam has exposed a silted landscape in an historic 26-foot drawdown. This has got me thinking about the primary difference between Columbia River dams like Wanapum, Chief Joseph and Rock Island – those operated as “run-of–the-river” facilities – and the storage dams on the Columbia in Canada.

Run-of-the-river dams have small reservoirs. They capitalize on the natural hydraulics of the Columbia’s snow-charged river system. Most of the American dams on the Columbia’s main stem generate power not from stored head, but from water passing regularly through the system. In order for water to be available at these facilities in fall and winter when demands are higher, the annual spring surge of the snow-charged Columbia must be stored somewhere.

The only Columbia storage in the United States is Lake Roosevelt, behind Grand Coulee Dam. Each year, the U.S. Bureau of Reclamation draws water down to accommodate snowmelt. The level varies, depending on weather. In 2013, it was approximately 25 feet from full pool, more or less equal to that experienced this year by Wanapum Dam in an emergency situation. In 2014, it has been approximately 55 feet.

Heading upstream into Canada, the typical drawdown increases. The Columbia River Treaty, signed in 1961 and ratified by both countries in 1964, governs water storage on the Canadian portion of the Columbia system. This storage makes American run-of-the-river projects fruitful, and protects urban areas on the lower and mid-Columbia from spring flood.

Between 1964-74, Canada built three major treaty storage dams. Under the terms of the treaty, Arrow Reservoir (near Castlegar, British Columbia) fluctuates up to 66 vertical feet annually. Duncan Reservoir near Kootenay Lake varies 98 feet. Kinbasket Reservoir, 85 miles north of Revelstoke, changes up to 195 vertical feet. In spring, if Kinbasket has been drained low to accommodate a large snowmelt, a visit to the “beach” can mean a long walk to the water.

Moderate or more extreme, drawdown numbers in Canada are considerably larger than what has been experienced at Wanapum. The treaty requires Canadian reservoirs to store 15.5 million acre-feet of water annually. The size of the reservoirs indicates just how wet and prolific the upper Columbia region in Canada is, contributing an average of 40 percent of the annual water flow through the international system – closer to 50 percent in a dry year.

The extreme changes in Canadian reservoirs have had a significant ecological and social/cultural impact. When the treaty was signed, those living in upper Columbia valleys experienced more impact due to the new water storage plans than people living on the mid- or lower Columbia. Many were displaced, or lost farms and livelihoods. Today, displaced families who still live in the region are reminded annually of the loss, when their farm fields, favored fishing spots, once-treasured wetlands and other landscape features are exposed as piles of inert and shapeless reservoir silt.

When they fill, the Canadian reservoirs create uniformity where diversity once existed. They silence the river system when, naturally, it would be most active – recharging wetlands with spring melt, carrying fish fry around, stirring up silt. Back-eddies, canyons, sand and gravel bars, alluvial fans and other varied, topographical features of a natural river are covered by late spring, not to be exposed again until the depths of winter, a reverse of the natural dynamics.

Each year, the landscape of a drained reservoir is exposed like an old family secret, providing an unpleasant reminder that hydroelectricity is not always green or benign. Those Americans living along Lake Roosevelt can understand this, too. Concrete dams on the upper Columbia have upended an ecological system thousands of years old.

Treaty storage reservoirs enhance and secure U.S. irrigation, flood control and hydroelectricity. The calculation of benefit-sharing in the treaty (the Canadian Entitlement) was accepted by both countries 50 years ago as a principle of fairness. Since then, the U.S. has made key decisions to protect endangered salmon, respect tribal interests and alter the predicted energy mix. These changes were imposed on the American river system by Americans.

They increase rather than decrease the value of the water Canada stores.