A stream is considered imparied when it is not fully supporting aquatic life and other beneficial uses.

As summarized in the TMDL documents, there are four main categories of pollutants that impact water sources within the Lake Helena Watershed:

A TMDL stands for “Total Maximum Daily Load”. This describes the maximum amount of any pollutant that a body of water can receive while still meeting water quality standards.


Streambank erosion is an inherent part of channel evolution and can contribute significant quantities of sediment to stream system sediment loads based on a combination of climatic and physiographic features. However, anthropogenic impacts, such as grazing, mining, timber harvest, road encroachment, riparian vegetation removal, and/or channel alterations can result in elevated rates of streambank erosion.

Sediment is the solid material carried in the streams. The sediment load in a stream depends on the degree of erosion and the flow of the stream.

Excessive levels of sediment cover prohibits fish spawning and insect habitat, fills pools, and alters stream channel morphology.

On average, sediment loading in the Lake Helena Watershed is about 47% above the naturally occurring level.

Unpaved roads, barren stream banks, timber harvest, and abandoned mining are the significant sources of sediment in the watershed.

Twelve streams in the Lake Helena Watershed do not meet their full potential to support fish and aquatic life:

  • Clancy Creek – headwaters to the mouth
  • Corbin Creek – headwaters to the mouth
  • Jennie’s Fork – headwaters to the mouth
  • Lump Gulch – headwaters to the mouth
  • Middle Fork Warm Springs Creek – headwaters to the mouth
  • North Fork Warm Springs Creek – headwaters to the mouth
  • Warm Springs Creek – Middle Fork to the mouth
  • Prickly Pear Creek – headwaters to Lake Helena
  • Sevenmile Creek – headwaters to the mouth
  • Skelly Gulch – headwaters to the mouth
  • Spring Creek – Corbin Creek to the mouth
  • Tenmile Creek – headwaters to the mouth


Nitrogen and phosphorous are chemical elements that promote the growth of plants and algae in streams and lakes. Nutrients are important and essential, but too much leads to overgrowth of algae and aquatic plants that eventually die. When they begin to decay, bacteria begins to break down the plant material and uses up a lot of the dissolved oxygen in the water. This depletes the oxygen that was once available for other organisms such as fish, resulting in an inhabitable stream. This excess of nutrients, plant/algae bloom and oxygen depletion is known as eutrophication.

The amount of nutrients entering the stream will vary depending on the season.

Fertilizer runoff, leaky septic systems, wastewater discharge and storm water runoff are major sources of nutrients in the watershed. These sources include both point sources, such as sewage treatment plants, and non-point sources, such as fertilized lawns and crop fields, septic systems, livestock and other animals.

Five water bodies in the Lake Helena Watershed have excessive amounts of nitrogen or phosphorous that beneficial uses of the water bodies have been impaired:

  • Prickly Pear Creek – Lump Gulch to mouth
  • Sevenmile Creek
  • Spring Creek– below Corbin Creek
  • Tenmile Creek
  • Lake Helena


Metals such as arsenic, cadmium, copper, lead and zinc are also essential but very harmful to both human and aquatic life health when concentrations are too high. Metals are often toxic to fish and other aquatic biota at much lower concentrations than they are to humans.

Metals occur naturally in the rocks and soils within the watershed. However, the abnormally high concentrations of metals can be a result of a large number of exposed, historic mining sites. Exposed ore, waste rock and mine tailings erode and wash into streams.

Learn more about Arsenic and Uranium in the Lake Helena Watershed

There are sixteen water bodies within the Lake Helena Watershed that are impaired from elevated concentrations of arsenic, cadmium, copper, lead and zinc.

  • Corbin Creek
  • Clancy Creek
  • Golconda Creek
  • Jennie’s Fork
  • Granite Creek
  • Jackson Creek
  • Middle Fork Warm Springs Creek
  • North Fork Warm Springs Creek
  • Warm Springs Creek
  • Lump Gulch
  • Prickly Pear Creek
  • Tenmile Creek
  • Sevenmile Creek
  • Silver Creek
  • Spring Creek
  • Lake Helena

    Water Temperature

    Water temperature controls the type and amount of biological organisms (fish, aquatic insects, microorganisms) in a stream. All organisms have an optimum temperature range for survival. Rates of other organic and inorganic processes are temperature-dependent as well. With increasing temperature, algae and plants increase can lead to eutrophication as discussed in the ‘Nutrients’ section. Fish populations could eventually shift from cold-water species to warm-water species.

    Shade from vegetation (such as taller shrubs and trees like willows and cottonwoods) is very important in keeping water temperatures lower. Removal of trees and shrubs from stream banks increases stream temperatures. Water diversions also lead to less water in the streams in the summer months, which results in higher water temperatures.

    Impaired by warmer water temperatures:

    • Prickly Pear Creak – downstream from Lump Gulch to Lake Helena

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