For years, it bedevilled Manitoba's relationship with North Dakota, spawning court cases, appeals to international commissions, high-level summits in Washington and a war of words between then-premier Gary Doer and North Dakota's governor.
Now, the outlets that drain Devils Lake into the Red River watershed raise barely a peep, and most of the feared effects have been modest -- so far.
Last summer was the first year both outlets, including the new east one, operated at full tilt to reduce remarkably high water levels on Devils Lake that have swamped farmland and homes.
'We did see it pretty clearly in the data. It's an ongoing concern for us'
The two outlets empty into the Sheyenne River, which then empties into the Red, both part of a different watershed than Devils Lake. For years, as North Dakota prepared to operate the outlets, the Manitoba government and many others feared contaminants -- nutrients, sulphates, foreign organisms such as fish parasites -- would be introduced into the Red River watershed, causing ecological damage.
So far this summer, both outlets have been running at full capacity for about three weeks, said Jon Kelsch of the North Dakota State Water Commission, and Manitoba has again been monitoring Red River water quality carefully.
The big issue is sulphates -- salts that can give drinking water a bitter taste and act as a laxative.
Starting last summer, the Red River saw noticeably elevated levels of sulphates as a result of the two outlets, though the levels were still within the province's drinking-water guidelines.
"We did see it pretty clearly in the data," said Manitoba water science and management director Nicole Armstrong. "It's an ongoing concern for us."
There are water-quality limits that govern the two outlets, meaning North Dakota must reduce the flow if sulphate levels get too high, but the lake typically has exponentially higher sulphate levels than the Red.
Two water-treatment plants in southern Manitoba -- one in Morris and another in Letellier -- draw their drinking water from the Red. The plant in Morris uses an additional membrane technology to treat the water so it can handle the extra sulphates. But the Letellier plant has struggled and might eventually need an upgrade.
"At the end of the year, the hardness level and the total organic carbon of the treated water were difficult to treat," wrote staff in the Pembina Valley Water Cooperative's 2012 annual report. "This is due to the high influence of the Devils Lake water in the Red River."
Also an issue are nutrients, which cause the gunky blue-green algae that is harming Lake Winnipeg. Armstrong said North Dakota has agreed to work on a joint nutrient-reduction plan.
Devils Lake is not a huge contributor of nutrients to Manitoba waterways, but no single source is, making it important to reduce even the small ones.
Last summer, both outlets sent nearly 200 million cubic metres of water into the Sheyenne watershed. In the fall, when the water hit Manitoba and the Red's levels were low, Devils Lake water made up half to two-thirds of the water in the Red.
In June, the latest flow data available so far this summer, about two million cubic metres of water flowed through the outlets.