Island Park Lake
Fremont County, Idaho8,680 acresView mapDirections
Nutrients and algae run above the regional average.
↓ down from C at the last regrade
- Eutrophic
- #1 of 3 in the county
- Public access
- Limited data
Island Park Lake in Fremont County, Idaho has a water quality grade of D (Nutrient-rich). Water clarity: 9.8 ft visibility. Phosphorus: 24 µg/L. Chlorophyll-a (algae): 11.8 µg/L. Surface area: 8680 acres.
- Clarity
- 9.8 ft
- Area
- 8,680 acres
- Type
- Eutrophic
- Phosphorus
- 24 µg/L
- Chlorophyll-a
- 11.8 µg/L
- Trend
- ↑ Improving
- Public access
- Yes
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Stays near Island Park Lake
Compare lakeside cabins, hotels, and vacation rentals near Island Park Lake in Fremont County, Idaho — 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 grade measures nutrients and algae, not lodging — cabins and rentals around Island Park Lake are listed below.
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Island Park Lake is a 8,680-acre productive, nutrient-rich eutrophic lake in Fremont County, Idaho. Water quality is graded D based on 2 sampling years through 2024. Overall water quality is improving over recent sampling years. Limited fish-species data available. Public access is available with 2 public boat landings. Compared to the 2 other monitored lakes in Fremont County, Island Park Lake ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, IDEQ, last sampled 2024-05-21. Grade methodology: LakeQuality methodology.
What Island Park Lake is good for
From access and monitoring records, not editorial picks.
- Clear water9.8 ft of visibility
- Boat launch2 documented ramps
- Camping1 public campground nearby
- Big water8,680 acres
Swimming Safety
Grade onlyLimited data
Based on clarity and algae grades from past sampling — we do not hold live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
The D is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
Water Quality Grade: D (Nutrient-rich)
Moderate clarity, visible to about 9.8 ft. Phosphorus 24 µg/L. Chlorophyll-a 11.8 µg/L. TSI 50. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 9.8 ft | Not graded |
| Phosphorus | 24 µg/L | Fair |
| Chlorophyll-a (Algae) | 11.8 µg/L | Poor |
| Trophic State Index (TSI) | 50 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 8,680 acres |
| Public Access | Yes |
No bathymetric survey has been published for Island Park Lake, so its depth is not documented here.
Recreation & Access
- ButtermilkPublic
- Mill CreekPublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Public campgrounds near Island Park Lake
- Buttermilk Campground2.3 km
Nearest public campgrounds in the USGS National Map inventory, within about 3 miles. An empty list means USGS records no campground that close, which is not the same as camping being unavailable. Where the source gives an official reservation link, it is used; the cabin and hotel search does not cover campsites. More camping lakes
Fishing Island Park Lake
Water Quality Trend: ↑ Improving
Based on 5 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.263 m/yr | 5 |
| Phosphorus | ↑ Improving | -1.15 µg/L/yr | 5 |
| Chlorophyll-a | ↑ Improving | -2.59 µg/L/yr | 5 |
Reservoir Info (USACE NID)
Island Park Lake is a man-made reservoir impounded by the Island Park Dam (completed 1938), built primarily for irrigation on the Henrys Fork; earth-type dam, 94 ft tall and 9,448 ft long.
- Surface area
- 8,680 ac
- Normal storage
- 127,646 ac-ft
- Max storage
- 169,646 ac-ft
- Drainage area
- 494.11 sq mi
- Hazard class
- High
- Owner
- BUREAU OF RECLAMATION
Source: USACE National Inventory of Dams, NID ID ID00272 · Operator website
County Ranking
Ranked #1 of 3 lakes in Fremont County
Nearby Lakes in Fremont County
Frequently asked questions about Island Park Lake
Where is Island Park Lake?
- Island Park Lake is a lake in Fremont County, Idaho. LakeQuality grades it D for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Island Park Lake?
- Island Park Lake in Fremont County, Idaho has a water quality grade of D (Nutrient-rich). Water clarity: 9.8 ft visibility. Phosphorus: 24 µg/L. Chlorophyll-a (algae): 11.8 µg/L. Surface area: 8680 acres.
Is Island Park Lake safe to swim in?
- The D is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
Are there boat ramps on Island Park Lake?
- Island Park Lake has 2 documented boat landings in the USGS National Boat Ramps inventory. Named access points include Buttermilk, Mill Creek. Public access is listed as yes.
Are there campgrounds on Island Park Lake?
- Island Park Lake has 1 public campground from USGS The National Map within 5 km, including Buttermilk Campground. This is a location join, not a booking. Cabins and hotels are listed separately; campsite reservations use the official link when the source provides one.
Explore Island Park Lake across LakeQuality
2 documented falls within 18 mi, nearest Upper Mesa Falls
2 thermal springs within 24.1 mi, nearest Ashton Warm Spring
Species activity outlook by water temperature and season
Where to stay at Idaho's top lakes, each with its grade
High nutrients, frequent algae, reduced clarity
Idaho's cleanest and most-polluted lakes, ranked
More Idaho Lake Rankings
Other Grade D Lakes in Idaho
Eutrophic Lakes in Idaho
Where this data comes from
34 measurements from 1 monitoring station, 2012–2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Bureau of Reclamation
1119USBR_WQX34 samples · 2012–2024
Analytical methods
- Depth, Secchi disk depth
- Zebra/Quagga Mussel APHA 10200G Modified
- 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.
Other records on this page
Named boat-access points from the USGS National Boat Ramps inventory
Public campgrounds from USGS The National Map Structures, within about 3 miles