Island Park Lake
Fremont County, Idaho8,680 acresView mapDirections
Idaho DEQ publishes the water-quality measurements for Island Park Lake. Here is what has been measured.
- Eutrophic
- Public access
- Limited data
Island Park Lake in Fremont County, Idaho has water-quality measurements published by Idaho DEQ, shown here as reported. Water clarity: 9.8 ft visibility. Phosphorus: 24 µg/L. Chlorophyll-a (algae): 11.8 µg/L. Surface area: 8680 acres.
Island Park Lake is a 8,680-acre productive, nutrient-rich eutrophic lake in Fremont County, Idaho. 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. Methodology: how these readings are compared.
At about 8,700 acres, Island Park Lake is large enough that where you stay decides which shore you see most of. It has 2 public boat landings, so a lakefront rental is not the only way to get a boat on the water. Vrbo is where to look for cabins and lake homes around Island Park Lake, and Booking.com and Expedia search hotels near the lake for your dates.
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 conditions
Readings onlyLimited data
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. Check local advisories before you swim.
Whether Island Park Lake is safe to swim in today is a call for the Idaho Department of Environmental Quality and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Island Park Lake
These are the measurements Idaho DEQ publishes for Island Park Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Moderate clarity, visible to about 9.8 ft. Phosphorus 24 µg/L. Chlorophyll-a 11.8 µg/L. TSI 50.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 9.8ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 24µg/L | Fair GoodFairPoor |
| Chlorophyll-a (algae) | 11.8µg/L | Poor GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 50 | Eutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
High nutrients, frequent algae, reduced clarity
Ask about Island Park Lake
Answers come straight from the public measurements and survey records on this page.
Lake Details
Surface area
8,680 acres
Public access
Yes
Listed by Idaho DEQ
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
- Buttermilk2.0 kmReserve
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
Stays via Stay22
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 readings cover nutrients and algae, not lodging. Cabins and rentals around Island Park Lake are listed below.
Top-rated places to stay near Island Park Lake
Prices for Oct 30–Nov 1, 4 adults. Change dates on the map below.
Availability and prices from Stay22 partners (Booking.com, Vrbo, Expedia). We may earn a commission from bookings, at no extra cost to you.
Planning a trip? Cabins and lodging at Island Park Lake → · more Idaho lake trips
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Fishing Island Park Lake
Water Quality Trend: Improving
Based on 5 years of monitoring (2012–2019).
Water clarity
Improving5 years
Phosphorus
Improving-1.15 µg/L/yr5 years
Chlorophyll-a
Improving-2.59 µg/L/yr5 years
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
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. Its water-quality measurements are published by Idaho DEQ and shown on this page as reported.
What is the water quality of Island Park Lake?
- Island Park Lake in Fremont County, Idaho has water-quality measurements published by Idaho DEQ, shown here as reported. 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?
- Nutrient and algae readings are 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.
Can I fish at Island Park Lake?
- Island Park Lake has 2 documented boat landings in the USGS National Boat Ramps inventory. Seasons, size and bag limits, and whether you need a license are set by Idaho's fish and wildlife agency, so check its current regulations before you go.
Are there campgrounds on Island Park Lake?
- Island Park Lake has 1 public campground from USGS The National Map within 5 km, including Buttermilk. 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 readings
Idaho's cleanest lakes, ranked on agency measurements
More lakes in Idaho
Other 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)
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
Named boat-access points from the USGS National Boat Ramps inventory
Public campgrounds from USGS The National Map Structures, within about 3 miles