Lake Helena Outlet
Lewis and Clark County, MontanaView mapDirections
Montana DEQ publishes the water-quality measurements for Lake Helena Outlet. Here is what has been measured.
- Hypereutrophic
- Impaired · Metals (other than mercury)
Lake Helena Outlet in Lewis and Clark County, Montana has water-quality measurements published by Montana DEQ, shown here as reported. Phosphorus: 115.5 µg/L.
Lake Helena Outlet is a highly nutrient-loaded hypereutrophic lake in Lewis and Clark County, Montana. Overall water quality is declining over recent sampling years. Compared to the 2 other monitored lakes in Lewis and Clark County, Lake Helena Outlet ranks #3 for water quality.
Source: EPA Water Quality Portal sampling records, Montana DEQ, last sampled 2023-10-17. Methodology: how these readings are compared.
Swimming conditions
Readings onlyElevated nutrients
Based on clarity and algae readings from past sampling — there is no live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
Nutrient and algae readings are not a swimming clearance. Lake Helena Outlet is listed impaired under Clean Water Act §303(d) (IR 4A) for metals (other than mercury), nutrients (phosphorus, nitrogen). Check local advisories before you swim.
Whether Lake Helena Outlet is safe to swim in today is a call for the Montana Department of Environmental Quality and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Lake Helena Outlet
These are the measurements Montana DEQ publishes for Lake Helena Outlet, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
No clarity data. Phosphorus 115.5 µg/L. TSI 73.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | No reading How deep a black-and-white disk stays visible from the surface. Higher is clearer. | |
| Total phosphorus | 116µg/L | Poor GoodFairPoor |
| Chlorophyll-a (algae) | No reading The green pigment in algae — a direct measure of how much algae is in the water. | |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 73 | Hypereutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Very high nutrients, dense algae, poor clarity
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Stays via Stay22
Stays near Lake Helena Outlet
Compare lakeside cabins, hotels, and vacation rentals near Lake Helena Outlet in Lewis and Clark County, Montana — live availability and prices for your trip. Switch the map to Satellite to see the lake and how close each stay is to the water. The water-quality readings cover nutrients and algae, not lodging. Cabins and rentals around Lake Helena Outlet are listed below.
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Fishing Lake Helena Outlet
Water Quality Trend: Worsening
Based on 5 years of monitoring (2019–2023).
Phosphorus
Worsening+17.15 µg/L/yr5 years
EPA Impairment Status
Lake Helena Outlet is officially listed as impaired under Clean Water Act §303(d) in the 2021 EPA reporting cycle (IR category 4A).
Causes of impairment
Designated uses not supporting: Drinking water, Aquatic life.
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit MT41I007_010 · Official waterbody report
Nearby Lakes in Lewis and Clark County
Frequently asked questions about Lake Helena Outlet
Where is Lake Helena Outlet?
- Lake Helena Outlet is a lake in Lewis and Clark County, Montana. Its water-quality measurements are published by Montana DEQ and shown on this page as reported.
What is the water quality of Lake Helena Outlet?
- Lake Helena Outlet in Lewis and Clark County, Montana has water-quality measurements published by Montana DEQ, shown here as reported. Phosphorus: 115.5 µg/L.
Is Lake Helena Outlet safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Lake Helena Outlet is listed impaired under Clean Water Act §303(d) (IR 4A) for metals (other than mercury), nutrients (phosphorus, nitrogen). Check local advisories before you swim.
Explore Lake Helena Outlet across LakeQuality
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Where this data comes from
30 measurements from 1 monitoring station, 2019–2023. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Montana DEQ WQPB
MDEQ_WQ_WQX30 samples · 2019–2023
Analytical methods
- Phosphorus by Colorimetry
- 4500 N C ~ Persufate Method for Total Nitrogen
Monitoring station identifiers (1)
EPA condition classes from the National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See where the data comes from and data sources.
Other records on this page
Impairment status from EPA ATTAINS 303(d) database