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SUBWATERSHEDS

The Thief River is a 1090 square mile watershed in northwestern Minnesota that is located within the Red River of the North watershed. The Thief River begins at the outlet of Thief Lake and flows along the western boundary of the watershed. Along the way, rivers and ditches(mostly ditches and channelized streams) that began at the eastern edge of the watershed flow nearly straight west and eventually contribute their water to the Thief River. Much of this water is temporarily stored in large pools like the Moose River Impoundment, Thief Lake, Agassiz, and the numerous other pools in and around Agassiz National Wildlife Refuge. The Thief River flows into the Red Lake River in Thief River Falls. The Red Lake River eventually empties into the Red River of the North in East Grand Forks.

According to the Thief River Watershed Monitoring and Assessment Report, land use in the Thief River Watershed is dominated by cropland (36%) and wetlands (44.9%). The remaining land cover distribution in the watershed is as follows:  7.8%range land, 6.7% forests, 2.8% developed, 1.7% open water, and 0.6%barren/mining. 

The main water quality issues in the Thief River watershed involve low dissolved oxygen levels, high turbidity and total suspended solids,high E. coli concentrations, and sedimentation.

An adequate supply of dissolved oxygen is important for the survival of fish and aquatic invertebrates. Low dissolved oxygen problems are found wherever water can become stagnant during the warm summer months. Two places where this is a common occurrence are the lower reaches of the Moose River and Branch 200 of Judicial Ditch 11.

Turbidity is measure of the amount of cloudiness in the water. High turbidity is a problem in the Thief River and Judicial Ditch 11downstream of the Agassiz Pool outlet. High turbidity levels can occur periodically on other reaches, but frequently or severely enough to exceed water quality standards. 2013 was the last year that the Thief River watershed will be officially assessed by the State of Minnesota using turbidity data. A water quality standard for total suspended solids (a parameter with a self-explanatory name) has replaced the turbidity standard. Sedimentation is a concern wherever a river flows into a reservoir (Thief Lake, Agassiz Pool, Thief River Falls Reservoir). Even if a river is not deemed impaired by high turbidity or total suspended solids, it still moves sediment. Dealing with that deposited sediment is a challenge for City of Thief River Falls and the Agassiz National Wildlife Refuge.

High E. coli concentrations from waterfowl, cliff swallows,livestock, wildlife, and other sources is a problem on some reaches within the Thief River watershed.  

For more than a century, the Thief River watershed has provided a conduit for drainage, making agriculture possible in many areas that were too wet to farm in pre-settlement times. Channels were dug and enlarge dusing coal-fired walking dredges. Pieces of coal used to fuel these machines can still be found along some of the dredged channels today.

The Thief River is a watershed in which there is some successful coexistence of agricultural practices and aquatic life. Despite the fact that approximately 96% of the channels in the Thief River have been channelized (man-made or altered by man), parts of the watershed provide great habitat for aquatic life. The pools in the watershed provide habitat for waterfowl and other wildlife. Many fish can be spotted heading upstream to spawn within some of the larger ditches. The lower Thief River supports a good fishery, especially where it hasn’t been channelized.

Whether a river or stream is natural or has been channelized, it still has to meet a set of water quality criteria. Good water quality is, of course, very important for the protection of aquatic life. Many people spend time swimming in the water in the Thief River and Red Lake River in and near the City of Thief River Falls to cool off during hot summer days.So, minimizing E. coli concentrations I the water is very important. The City f Thief River Falls utilizes water from the Thief River and Red Lake River as a source of drinking water for the city. The water I the Red Lake River is almost always cleaner than the water in the Thief River. So, if the water in the Thief River Falls reservoir has to be extensively treated by the city’s water treatment plant, the Thief River is usually the culprit. Downstream of Thief River Falls, the water is used for recreational tubing and swimming in Red Lake Falls and for drinking water in East Grand Forks.

Working to reduce erosion to minimize the amount of sediment and other pollutants in the rivers, streams, and ditches in the Thief River watershed is important for a number of reasons and from multiple perspectives.From an aquatic life perspective, excess sediment and sedimentation degrades aquatic habitat and can directly affect the health of aquatic organisms.

Pools and reservoirs within the watershed are negatively affected by excess sedimentation. There is a reasonable expectation that pools fed by rivers will eventually fill with sediment. Even rivers with relatively clean water can move a significant amount of sediment along the bed of the channel. Studies show that sedimentation has been increased above natural levels, however. This has resulted in the need for hydraulic dredging of the Thief River Falls Reservoir. Agassiz Pool, within Agassiz National Wildlife Refuge, receives water from both the Thief River, Mud River (a.k.a. Judicial Ditch 11). It has been significantly affected by sedimentation over the years and the United States Fish and Wildlife Service has been working hard to find solutions to the problem.

On a smaller scale, landowner perspective, excess gullying and other types of erosion from fields deposits sediment within drainage ditches and reduces the drainage capacity of those ditches. The loss of drainage potential and the cost of ditch clean outs are preventable costs. Sedimentation should be minimized through the use of best management practices such as riparian (along the channel) buffer strips, side water inlets, wind breaks, and no-till practices.