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Restoring and Maintaining Water Quality and Aquatic Ecosystem Health at Voyageurs National Park through Bi-National Cooperation

Ash River entrance
Ash River entrance
NPS/CHRISTOPHER LIGHT

Water level management in Rainy Lake and the Namakan Reservoir is the most significant natural resource issue for Voyageurs National Park. Water management in these border lakes is also a significant resource issue for multiple State, Provincial, and Federal (both Canadian and United States) resources management agencies. The water levels in these lakes are controlled by a privately owned hydropower dam at the outlet of Rainy Lake and by regulatory dams on the two outlets from Namakan Lake that supply Rainy Lake. Prior to installation of the dams in the early 1900s, all of these lakes existed as natural water bodies. Flows are now regulated to satisfy multiple uses, including power generation and recreation. Because these lakes are international waters, the International Joint Commission (IJC) has regulatory authority and stipulates water management practices (rule curves) to the private sector dam operators. Rule curves are bands of allowable high and low water levels throughout the year.

During 1970-1999, the "1970 Rule Curves" were in effect, by which larger-than-natural fluctuations in water levels of the Namakan Reservoir were used to maintain smaller-than-natural fluctuations in water levels of Rainy Lake. In the 1980s, Voyageurs initiated research on effects of water level management on the aquatic ecosystem of the park in order to develop alternatives to the 1970 Rule Curves. Research centered on the effects of dam operations on the reproductive success of walleye, northern pike, and whitefish. Analysis of historic commercial fish-catch and water-level data found that fluctuations in fish catches were tightly linked to water-level fluctuations and that the population dynamics of fish were more disturbed in Namakan Reservoir than in Rainy Lake, relative to nearby natural (undammed) Lac La Croix. Lac La Croix also supported a more diverse aquatic plant community than either Rainy Lake or Namakan Reservoir. Water quality differences were also expected in the regulated lakes compared to undammed lakes, because water-level fluctuations affect nutrient exchange and cycling.

The results of the Voyageurs research program and other studies were used by a committee of U.S. and Canadian representatives from private industry, the public and government agencies to develop a consensus on water management in the Rainy Lake-Namakan Reservoir system. This group submitted recommendations to the IJC in 1993. The IJC evaluated the recommendations and concluded that modifications to the 1970 Rule Curves were justified.

Black Bay off Rainy Lake
Black Bay off Rainy Lake
NPS/CHRISTOPHER LIGHT

In January 2000, the IJC issued a new Supplementary Order for the hydrological management of the Rainy Lake-Namakan Reservoir system. This order prescribes the 2000 Rule Curves, which specify water level fluctuations that are more similar to pre-dam hydrology than were the 1970 Rule Curves. The IJC order stipulates that the 2000 Rule Curves will be reviewed in 2015 giving consideration to "monitoring information collected by natural resource management agencies and others during the interim that may indicate the effect of the changes..."

In response, Federal, Provincial, and State agencies in Canada and the United States with management interests in this system contributed significant funding, research, and monitoring to assess the effects of the 2000 Rule Curves, including research on water quality (especially mercury cycling, trophic state, and nutrient loading) and multiple other ecological indicators including fish, aquatic vegetation, aquatic macroinvertebrates, furbearers, and common loons. Additionally, in response to a request from these agencies, the Canadian and United States governments have funded a suite of studies through the IJC to fill the remaining high priority gaps in knowledge of the effects of this change in rules prior to 2015. The suite of studies is managed by two Voyageurs National Park Aquatic Ecologists and includes monitoring and research focused on hydrologic effects of the change in rules governing dam operation and on many ecological, cultural resources, and economic indicators. Although most of these studies are incomplete, results from completed studies indicate that for the lakes of Namakan Reservoir, where the rule change was most pronounced, aquatic vegetation communities and benthic macroinvertebrate communities are recovering. Voyageurs National Park resource managers look forward to providing comprehensive research and modeling results to the International Joint Commission prior to the 2015 Review of the 2000 Rule Curves in order to best protect and maintain the water quality and aquatic ecosystem of the park.

Last Updated: March 14, 2013