Island Park Reservoir, Idaho, USA

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USA - West - Idaho - Eastern -

Just half an hour southwest of west Yellowstone, MT, Island Park Reservoir hosts a recreational paradise all its own. The roughly 7000-ace reservoir is formed by the dam built across Henry’s Fork, a Snake River tributary. The dam, completed in 1939, allows for water storage to provide irrigation waters to the thirsty Snake River Plain.

As part of the massive Minidoka Project which includes the Minidoka Dam and power plant, Lake Wolcott, Jackson Lake Dam, American Falls Dam and Reservoir, Grassy Lake Dam, diversion dams, canals and nearly 200 water supply wells, Island Park Reservoir provides primarily water storage and recreation. Originally, a small hydropower plant provided electricity to workers building the dam and later to nearby resort properties. Although there has been some discussion of retrofitting the dam for power production, it isn’t clear that this has yet been accomplished. The United States Bureau of Reclamation owns the dams and has overall control of the project. Island Park Reservoir lies within the Caribou-Targhee National Forest. The US Forest Service operates several campgrounds and boat ramps along the 64-mile shoreline.

After 75 years of existence, Island Park Reservoir has developed some fine recreational opportunities. Four major boat ramps provide boat access for water skiing, pleasure boating, tubing, sailing, windsurfing, jet skiing, kayaking, pontooning, canoeing and fishing. Although water levels fluctuate, one or two ramps are passable even during periods of low water. The community of Island Park has developed along the shore of the large island near the east end of the reservoir and along Henry’s Fork, where many residents enjoy vacation homes and year-round living. Many of the upscale homes are available as short-term rentals. A few resort facilities are located near Island Park with cabins and lodge rooms. Some of these resort facilities also rent boats, pontoons and paddle craft. Most needed supplies can be purchased in Island Park.

Fishing is a big draw to Island Park Reservoir. The waters hold kokanee, whitefish, cutthroat trout, rainbow trout, coho salmon, bluegill and yellow perch. Although the best fishing is usually by boat, some limited shore fishing is available near the boat ramps. The creeks flowing into the reservoir are highly-productive trout streams. Ice fishing takes over in winter. Indeed, winter sports in the area are nearly as popular as summer activities, with the area holding nearly 500 miles of trails for snowmobiles and cross-country skiing. The area abuts other state and federal lands, and a wealth of trail systems allows for mountain biking, hiking and nature study.

Lands south of the reservoir are primarily located within the national forest, while those north of the reservoir are remote and sparsely populated. National forest campgrounds are spread along the southern shoreline, while a few year-round camping cabins are remotely located. In winter, these cabins can only be reached by snowmobile. The campgrounds usually have a small swimming area, and most are adjacent to boat ramps so campers can easily bring their boat with them. Dispersed primitive camping is permitted in some areas. Motels in the village of Island Park usually stay open most of the year to provide lodgings to winter sports enthusiasts.

Just a short distance downstream along Henry’s Fork, Harriman State Park provides for camping and river fishing. There is a wealth of nature to observe within the 18,000-acre wildlife refuge designated here within the Greater Yellowstone Ecosystem. Both black bears and grizzly bears can be found in the area, along with elk, moose, sandhill cranes and trumpeter swans. The entire area surrounding Island Park Reservoir is a popular spot for outdoor recreation; guest ranches, rental cottage communities and small bed & breakfasts offer such amenities as horseback riding, guided fishing and whitewater rafting and back-country camping.

Island Park Reservoir occupies part of the world’s largest collapsed volcanic caldera: 23 miles across, the ancient caldera is part of the same geophysical system that created nearby Yellowstone National Park a few miles to the east. The topography is similar, heavily forested with lodgepole pines and overlooked by several scenic peaks. Island Park Reservoir with its many campgrounds and lakeside lodging opportunities makes the ideal place to spend a family vacation that includes visiting Yellowstone on a day trip. National efforts to assign National Monument status to the reservoir and its surroundings have been met locally with strong resistance. Property owners and businesses fear interference in the form of additional restrictions on their use and enjoyment of their properties, with corresponding difficulties in conducting business as has been historically done here. It remains to be seen how the situation will be resolved.

National Forest Ranger Stations, including the one in Island Park near the dam, contain detailed maps of the many trails, campgrounds and other recreational venues in the area. A small fee is charged for some activities and for camping. All Idaho fishing regulations are in force as well as the occasional, special regulation for certain species to protect spawning fish. Because of the wild nature of the back country area, all campers are encouraged to secure all food supplies in bear-proof containers. Campfire regulations vary according to location and weather conditions. Not all campsites have electricity or potable water available, so it is best to consult National Forest Service maps and publications before planning your trip.

If Yellowstone National Park has been on your vacation radar but you dread the crowds and tight schedules, then Island Park Reservoir and its wide range of lodgings is for you. Whether you pack the tent, pull an RV, or opt for a full-service resort or vacation rental home, there are lodgings here for you.

* The only depth listed for Island Park Reservoir is the depth at the dam. We have used that as the maximum depth. Elevation may also change depending on water levels.

Things to do at Island Park Reservoir

  • Vacation Rentals
  • Fishing
  • Ice Fishing
  • Boating
  • Sailing
  • Swimming
  • Canoeing
  • Kayaking
  • Whitewater Rafting
  • Jet Skiing
  • Water Skiing
  • Tubing
  • Camping
  • Campground
  • Cabin Rentals
  • Hiking
  • Biking
  • Cross-Country Skiing
  • Snowmobiling
  • Horseback Riding
  • Wildlife Viewing
  • State Park
  • National Park
  • National Forest

Fish species found at Island Park Reservoir

  • Bluegill
  • Coho Salmon
  • Cutthroat Trout
  • Kokanee Salmon
  • Perch
  • Rainbow Trout
  • Salmon
  • Sunfish
  • Trout
  • Whitefish
  • Yellow Perch

Island Park Reservoir Photo Gallery

Island Park Reservoir Statistics & Helpful Links

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Lake Type: Not Known

Water Level Control: U.S. Bureau of Reclamation

Surface Area: 7,000 acres

Shoreline Length: 64 miles

Normal Elevation (Full Pond): 6,302 feet

Maximum Depth: 75 feet

Water Volume: 135,500 acre-feet

Completion Year: 1939

Drainage Area: 482 sq. miles

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Trophic State | LakeLubbers

Trophic State measures the level of algae and nutrients in a lake.

An oligotrophic lake is very clear (blue in color) and does not support much plant or fish life. A hyper-oligotrophic lake is the clearest of all lakes, and is nearly devoid of plants and fish.

A mesotrophic lake is slightly green and supports a moderate degree of plant and fish life. A lake's most desired trophic state is generally this mid-point - the mesotrophic state.

A eutrophic lake is somewhat murky and supports a large amount of plant and fish life. A hypereutrophic lake is clouded with algae, plant life, and fish life. A eutrophic or hyper-eutrophic lake can be difficult to navigate by boat - and is often an unpleasant place to swim.

The use of phosphorus-rich and nitrogen-rich fertilizer on lawns and golf courses surrounding a lake can cause it to become eutrophic or hypereutrophic.


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Catchment or Drainage Area | LakeLubbers

This is the surrounding area that drains into a lake, including land, rivers and their tributaries. This is also known as the lake's "catchment basin".

Small lakes at the highest peaks of mountains have small drainage areas. The world's oceans have the largest drainage areas.


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Lake-Area Population | LakeLubbers

This is the estimated number of people who live in a house with a view of a lake, plus those who self-describe the lake as their home, for example: "I live at Smith Mountain Lake."


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Water Residence Time | LakeLubbers

This is the estimated time that it takes for an amount of water equal to the entire volume of a lake to flow out of - or evaporate from - the lake.

Residence Time can be as short as a few days for fast-flowing small lakes, and can exceed 100 years for slow-flowing large lakes.


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Completion Year | LakeLubbers

This is the year that a reservoir was first filled to the reservoir's normal elevation - or the year that a natural lake was first dammed. A large reservoir can take more than a year to fill after its dam is first closed.

The Grand Anicut in southern India is generally considered the world's oldest dam that still operates. Grand Anicut was constructed in the second century BC. It now impounds an irrigation network that includes roughly one million acres.

You can find many of the the world's newest reservoirs on LakeLubbers. Many of the world's oldest reservoirs appear on the last page of that list.


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Water Volume | LakeLubbers

This is the estimated volume of water that a lake contains -- measured at the lake's normal elevation. By this measure, the world's largest freshwater lake is Siberia's Lake Baikal.

You can find many of the the world's largest lakes (by water volume) on LakeLubbers.

Water Volume can be measured in acre-feet, in cubic miles, or in cubic kilometers. One acre-foot is the amount of water needed to cover one acre (43,560 square feet) to a depth of one foot. One cubic mile equals 3,379,200 acre-feet. One cubic kilometer equals 810,713 acre-feet.

1 acre-foot is equal to 325,851 US gallons. Siberia's Lake Baikal contains about 6,276,367,740,000,000 gallons of freshwater - nearly 1 million gallons for every living person on earth.

The other - and more widely used - measure of a lake's size is the lake's surface acreage. By that measure, the world's largest freshwater lake is North America's Lake Superior.


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Maximum Depth | LakeLubbers

This is the estimated greatest depth of the water in a lake -- measured at the lake's normal elevation. The world's deepest lake is Siberia's Lake Baikal; that lake's maximum depth is estimated at 5,314 feet.

You can find many of the the world's deepest lakes on LakeLubbers. If you select the last page of that list, you will find the (maximum depth of) the shallowest lakes in our database.


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Average Depth | LakeLubbers

This is the estimated average depth of the water in a lake -- measured at the lake's normal elevation. If the water volume and surface area of a lake are known, an estimate of the lake's average depth can be calculated:

Water volume ÷ Surface Area = Average Depth

Example: 1,000,000 acre-feet ÷ 20,000 acres = 50 feet average depth


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Maximum Elevation | LakeLubbers

This is a lake's highest water level, measured by the lake's surface distance above sea level, that can occur during flooding. A lake's highest possible maximum elevation is usually the top of the lake's dam or spillway.

At lakes that include residential development, government regulations usually forbid the construction of homes below a lake's maximum elevation.


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Minimum Elevation | LakeLubbers

This is a lake's lowest water level, measured by the lake's surface distance above sea level, that can be reasonably expected to occur. Low lake levels can occur due to deliberate seasonal draw downs for irrigation or impending snow melt, reduced water inflows, drought and evaporation, residential or commercial water demands, and hydropower generation.

Some lakes' minimum and maximum elevations are virtually the same. Lakes that generate hydropower may vary by several feet - according to power demand. Lakes whose primary purpose is to prevent flooding can seasonally vary by 100 feet or more.

When some lakes reach their minimum elevation, their boat ramps may not be long enough to permit boat access - and boats docked on shallow parts of the lake may end up on dry ground. In those cases, kayakers and shore-based anglers may be among the few happy recreational users of the lake.


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Normal Elevation | LakeLubbers

This is a lake's normal water level, measured by the lake's surface distance above sea level. For a reservoir, this water level is also known as "full pond" or "full pool".

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Shoreline Length | LakeLubbers

This is the length of the exterior shoreline around a lake - measured at the lake's normal elevation. The shoreline length can be considerably shorter or longer when lake water levels are lower or higher than normal.

A lake with many coves has a much longer shoreline than a lake of similar surface area that is nearly circular in shape.

When known, the shoreline miles that we report in our statistics include only the lake's exterior shoreline, and exclude the shorelines of islands located within a lake's boundaries. In lakes with many islands, those islands' combined shorelines may exceed a lake's exterior shoreline.

You can find many of the world's longest-shoreline lakes on Lakelubbers.


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Surface Area | LakeLubbers

This is the area (acreage, square kilometers, etc.) of the top surface area of a lake - measured at a lake's normal elevation. The surface area can be considerably smaller or larger when lake levels are lower or higher than normal. North America's Lake Superior is the world's largest freshwater lake by this measure.

The other measure of a lake's size is the lake's water volume. By that measure, the world's largest freshwater lake is Lake Baikal in Siberia.

You can find many of the world's largest lakes (acres) on Lakelubbers. There is no widely-accepted minimum surface area that defines a lake. What Lakelubbers describes as a lake, you might call a pond. The smallest lake that Lakelubbers currently includes is Hawaii's 2-acre Lake Waiau.


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Water Level Control | LakeLubbers

This is the organization that controls water releases or outflows from the lake or reservoir. In the USA, this is often the US Army Corps of Engineers, a power company, a municipal water system, an irrigation district, or a paper manufacturing company. In the case of private or gated lakes, a homeowners' association may be the lake's controlling authority.

Many lakes cross borders, including North America's Great Lakes. The control of such lakes and their coveted freshwater may be amicably shared - or hotly disputed.

"Water wars" continue at many lakes as growing populations and crop irrigation needs compete for the freshwater that lakes contain.


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Lake Type | LakeLubbers

There are 3 basic types of lakes that are currently included on LakeLubbers. 2 types may be dammed or not dammed, producing 5 classifications.

- A Reservoir is a man-made freshwater lake that is usually created by damming rivers.

- A Natural Freshwater Lake occurs naturally - often by glacial activity - and has a salinity of less than 30 parts per thousand. It may be dammed to produce electricity or for other reasons.

- A Natural Saltwater Lake occurs naturally and has a salinity of more than 30 parts per thousand (ppt). It may be dammed.

"Brackish" water may be categorized as freshwater or saltwater, depending on its salt content (salinity). Oligohaline water has less than 15 ppt of salt. Mesohaline water has 15-29 ppt. Polyhaline has 30-335 ppt.


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