Island Park Reservoir
Broadwater County, MontanaView mapDirections
Not enough samples to grade — no nutrient or algae measurement meets the evidence bar (at least 3 samples within 10 years). No letter yet. Here is what we do have.
- Limited data
Island Park Reservoir in Broadwater County, Montana is not rated for water quality — its monitoring record does not meet the evidence bar. Phosphorus: 23.5 µg/L. Chlorophyll-a (algae): 6.3 µg/L.
- Phosphorus
- 23.5 µg/L
- Chlorophyll-a
- 6.3 µg/L
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Watch Island Park Reservoir’s letter
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Why Island Park Reservoir has no grade
We grade a lake only when the monitoring record supports a letter: at least three phosphorus or chlorophyll-a samples in the last ten years, scored against EPA National Lakes Assessment thresholds for this lake’s ecoregion. For Island Park Reservoir, no nutrient or algae measurement meets the evidence bar (at least 3 samples within 10 years). Sampling here has recorded phosphorus and algae (chlorophyll-a), but not water clarity.
Not Rated is not an F. It is EPA Integrated Reporting Category 3 — insufficient information. The water here may be excellent or poor; nobody has measured enough of it to say. Everything below that has been measured is still reported on this page.
Sampling is run by Montana DEQ and volunteer programs, and published through the EPA Water Quality Portal. Read the full grading methodology.
Island Park Reservoir is a lake in Broadwater County, Montana.
Source: EPA Water Quality Portal sampling records, Montana DEQ, last sampled 2024-09-17. Grade methodology: LakeQuality methodology.
Swimming Safety
Not ratedLimited data
The letter is not a swimming clearance. Check local advisories before you swim.
Water quality measurements for Island Park Reservoir
These readings exist but are not enough for an A–F grade — see why.
No clarity data. Phosphorus 23.5 µg/L. Chlorophyll-a 6.3 µg/L. TSI 49.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No recent samples | |
| Phosphorus | 23.5 µg/L | Not graded |
| Chlorophyll-a (Algae) | 6.3 µg/L | Not graded |
| Trophic State Index (TSI) | 49 | Mesotrophic |
Moderate nutrients, good water quality
Fishing Island Park Reservoir
Graded lakes near Island Park Reservoir
Island Park Reservoir has no grade, but these lakes within a short drive do.
Nearby Lakes in Broadwater County
Frequently asked questions about Island Park Reservoir
Where is Island Park Reservoir?
- Island Park Reservoir is a lake in Broadwater County, Montana. LakeQuality has not rated this lake (UNRATED) — no nutrient or algae measurement meets the evidence bar (at least 3 samples within 10 years).
What is the water quality grade for Island Park Reservoir?
- Island Park Reservoir in Broadwater County, Montana is not rated for water quality — its monitoring record does not meet the evidence bar. Phosphorus: 23.5 µg/L. Chlorophyll-a (algae): 6.3 µg/L.
Is Island Park Reservoir safe to swim in?
- The letter is not a swimming clearance. Check local advisories before you swim.
Explore Island Park Reservoir across LakeQuality
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Where this data comes from
6 measurements from 1 monitoring station, 2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Bureau of Reclamation
1119USBR_WQX6 samples · 2024
Analytical methods
- Phosphorus by Single Reagent Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
- Turbidity by Nephelometry
Monitoring station identifiers (1)
Grade thresholds from the EPA National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See how grades are calculated and data sources.