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Nemadji River
Nemadji RiverThe Wild Nemadji
The Nemadji River and its tributaries flow through Minnesota and Wisconsin, draining approximately 433 square miles. Approximately 40% of the drainage basin is in Wisconsin. According to the Carlton, MN Soil and Water Conservation District (CSWCD), approximately 192,000 acres of the land is forested, or 69% of the watershed, with 53% of forested land consisting of deciduous trees greater than 45 years old.

The lower Nemadji River flows in a narrow, steep-sided valley when it enters the heavily industrialized and urbanized portion of the City of Superior; from there it empties into Allouez Bay and the Duluth-Superior Harbor near the Burlington Northern Ore Docks (WDNR). The major development near the river is a Burlington Northern Santa Fe Railroad taconite storage facility. Taconite pile rainfall runoff is collected on site where it passes into a series of detention ponds and discharges to the Nemadji River through a pipe.

Managing the Area
Detention ponds on the Nemadji Gold Course also detain surface runoff and provide management of area flows (CTE Surface Water Management Plan). Even within the City of Superior, the steep clay bluffs that confine the valley are generally undeveloped and forested in some places, creating a buffer between the river system and surrounding urban areas. A series of emergent marshes occur along the inside of the well-developed meanders that are characteristic of this river. These marshes are separated from the main channel by weedy natural levees, which support a mixture of tall wetland shrubs and small lowland hardwoods (WDNR).

The mouth of the Nemadji River is an area of side-channel wetlands that extend for about a mile upstream. Wetlands at the mouth of the Nemadji cover about 90 acres and support the spawning beds of over 60 warm water fish species, including muskellunge, perch, bass, walleye, northern pike, and salmon. Lamprey also occur in the river. This area is identified by the Lake Superior Binational Program as important habitat to the Lake Superior ecosystem for coastal wetlands as well as fish and wildlife spawning and nursery grounds.

The Murky Nemadji
The Nemadji River is famous for its turbid, clay-filled water. About 33% of the river’s basin is covered in red clay, sometimes up to 200 feet thick; this layer was deposited during a geologic period when glacial lakes covered the region (CSWCD). Though red clay erosion is natural, human activities on the land in the last century have accelerated the natural process, and the river has cut deep valleys into the surrounding bluffs. According to the Natural Resources Conservation Service (NRCS), movement of soil material downhill due to gravity (slumping) is severe. Nearly 90% of the fine sediment in the river is due to bluff erosion and slumping, and 74% of this sediment ultimately ends up in Lake Superior (CSWCD).

The major human activities that have had a significant impact on the hydrology of the Nemadji River basin are the early logging practices dating back to the mid 1800s. Logging converted forest to permanent agriculture, streams were cleared to efficiently transport logs to the sawmills,, and roads and railroads cut through the basin. This all led to efficient hydrologic pathways for water to get to the river quickly (Nemadji River Basin Project).

Area Trees
While approximately 70% percent of the watershed is now reforested, the deciduous trees adjacent to streams may not be an effective sediment filter, or may not form a sturdy enough root system to hold soils in place. Many red clay slumps in the watershed move downhill despite tree cover, likely due to shallow groundwater movement beneath the root zone. The riparian areas along the stream vary dramatically in width and quality (NRCS).

Transport of pollutants attached to settled bottom material has created a “storehouse” of toxins in the lower reaches of the harbor. Pollutants include mercury, dioxins, and polychlorinated biphenyls. Re-suspension and/or dredging of this material can lead to elevated toxin levels in the biota. Increased sedimentation also decreases the river’s fisheries. Even so, the Minnesota portion of the Nemadji watershed contributes 40% of Lake Superior’s migratory trout and salmon spawning habitat in Minnesota. In addition, fine-grained sedimentation degrades the quality of spawning bed habitat by covering fish eggs with fine-grained sediment (Nemadji River Basin Project).

The Expensive Nemadji
The Duluth-Superior Harbor is shallow, so it must be dredged to maintain channels deep enough for ship traffic. Approximately 33,000 tons of Nemadji River sediment is dredged annually by the U.S. Army Corps of Engineers to maintain adequate depth for shipping traffic in Superior Bay. The annual cost for this portion of the total dredging within the Duluth-Superior Harbor area is approximately $260,000 (WDNR Basin Plan). The Nemadji River deposits approximately 131,100 tons of sediment per year into the Harbor; of that amount, between 94,000 and 117,000 tons are silt and clay. This is the equivalent of 17 dump truck loads of silt and clay being unloaded into Lake Superior daily. Sedimentation can cause choking of spawning beds and carry contaminants and nutrients with them that can degrade aquatic habitat. (NRCS)

In addition, damage due to the instability of red clay results in frequent and expensive maintenance schedules for road cut and embankment situations. The most extensive study of damage to the ecosystem was done during the Red Clay Project in the 1970s. Property damage from slumping is relatively small due to the low population density in the watershed (WDNR Basin Plan).

The Susceptible Nemadji
As the Nemadji flows into the City of Superior, several railroads and highways cross over it. The susceptibility of the river to waste discharges and spills became clear when several Burlington-Northern railway cars fell from the Highway 35 Bridge into the river on June 30, 1992. One tank car ruptured, releasing 34,000 gallons of a chemical mixture known as aromatic concentrates. Benzene makes up about 45 percent of the chemical mixture. Approximately 30,000 people in the Superior area had to evacuate as a cloud of chemical vapors drifted over the city, portions of Duluth, and the western tip of Lake Superior (WDNR Basin Plan).

However, human health was not immediately threatened, though Superior Police Department prevented public access to the affected area and the Douglas County rescue squad patrolled the Nemadji River (EPA). Dying and distressed fish were observed in conjunction with the spill. Mortality estimates suggest thousands of fish died, including game, forage, and rough species. Distressed fish rose to the water’s surface where they were exposed to the sheen of raw chemicals and vulnerable to predation by the many gulls observed feeding on them (WDNR Basin Plan).

Spill Response
Stormy weather and safety issues hampered spill response. Heavy rains following the spill may have helped disperse the materials and cold weather reduced vaporization. Containment booms helped recover some chemicals at the 31st St Bridge, but rising water levels and mixing during the 16-mile run downstream inhibited recovery. Most of material reached Superior Harbor within 30 to 50 hours after the spill. Most contaminants quickly volatized or were carried away in the river, while some substances bound to sediments, where they dissipated more slowly. While many were concerned that residuals of the chemicals would linger in the river sediments, tests one year later showed no significant results (WDNR Basin Plan).

The City’s Comprehensive Plan suggests that approximately 500 new residential units will be constructed along the Nemadji River by 2020. The new impervious area could increase sediment loads to Superior Bay and create larger peak runoff rates and volumes (CTE Water Management Plan).

Rehabilitating the Nemadji
The Nemadji River is part of the St. Louis River Area of Concern (AOC), which was designated by the Great Lakes Water Quality Agreement (WQA) between the United States and Canada in 1972. Nine beneficial use impairments have been recognized:
  • Restrictions on fish and wildlife consumption
  • Degradation of fish and wildlife populations
  • Fish tumors or other deformities
  • Degradation of benthos
  • Restrictions on dredging activities
  • Eutrophication or undesirable algae
  • Beach closings
  • Degradation of aesthetics
  • Loss of fish and wildlife habitat

The Remedial Action Plan (RAP) was developed in 1987 to restore beneficial uses of this area. The goal of the RAP is to define problems and their causes, and then recommend actions and timetables to restore all beneficial uses of the AOCs. Restoring uses is to be achieved through implementation of programs and measures to control pollution sources and remediate environmental problems (St. Louis River Citizens Action Committee).

Reducing Sedimentation
In 1993, the Citizen’s Advisory Committee of the RAP requested the Natural Resources Conservation Service identify methods for reducing sedimentation in the Nemadji River (Nemadji River Basin Project, Phase II). The Nemadji River Basin Project (NRBP) began in October 1993. The effort is led by the Natural Resources Conservation Service, which applied for the funds with local sponsors (Carlton County Board, Douglas County Board, Carlton County Soil & Water Conservation District, Duluth/Superior Metropolitan Interstate Committee).

The RAP advised that agencies secure funding to implement recommendations generated by the NRBP. These recommendations will forward the goal of reducing sediment input from the Nemadji River watershed. The RAP calls for a basin project to reduce erosion and sedimentation, with a watershed-wide focus, determinations of the extent and causes of runoff problems, and strategies to implement practices that would reduce erosion and sedimentation. The NRBS builds on previous work of the Red Clay Project, which focused on engineering solutions to streambank erosion – they concluded that 90 percent of the sediment discharged to Lake Superior originated in 2 percent of the area, namely streambanks, channels, and gullies (WDNR Basin Plan).

Further Protecting the Water
As part of the NRBP, the WDNR has been involved in developing practices for land use, soil management, and forestry that will help protect and improve water quality condition. A detailed sediment budget was also developed for the watershed. Data provided by the project will be used to rank the basin for priority watershed selection, with the knowledge that the watershed could benefit from priority watershed status (Nemadji River Basin Project, Phase II).

Though the lower Nemadji system has suffered many abuses, it has retained significant natural features and should be a prime candidate for remedial attention. Protecting and rehabilitating the Nemadji River corridor is a priority, because it harbors ecologically unusual rich mesic hardwood forests, floodplain forests, and marshes. The marshes are representatively diverse, dominated by native species, appear reasonably functional, and support uncommon resident birds. Exotic plants are still quite localized, associated mostly with the disturbed levees and formerly dredged areas near U.S. Highway 2. The Nemadji River Bottoms are also identified as a Lake Superior Basin Priority Site due to its high quality floodplain wetlands and the erodability of the soils in this area.

Learn More
Nemadji River Watershed Map 
Pictures of the Nemadji River 
Monitoring Data