Arrowrock Reservoir, Idaho, USA

Lake Locations:

USA - West - Idaho - Southwestern -

One in a string of three major reservoirs built to irrigate the parched Boise Valley, Arrowrock Reservoir has contributed to water recreation in southwestern Idaho for nearly a hundred years. Arrowrock Dam was the tallest concrete arch structure in the world at 348 feet when completed in 1915, a title it held until 1924. Located at the confluence of the main channel and the south fork of the Boise River, the dam incorporated a series of new innovations into its preparatory work and construction. When completely filled, the reservoir stretched 18 miles up the canyon and covered 3,141 acres with water. When the dam was refurbished in 1937, another five feet in height were added to the dam. The ‘Y’-shaped reservoir extends back along both the south fork and the main fork of the Boise River. Although no absolute depths are recorded for the reservoir, depth is at least 260 feet at the base of the dam. Because the walls of the canyon are steep, actual depths within the reservoir are likely deeper in spots.

Arrowrock Reservoir is not heavily visited, despite being only a 30-minute drive from Boise. Steep canyon walls make access to much of the 60-mile shoreline difficult. Neighboring Lucky Peak Reservoir just a few miles downstream is equipped with more organized recreational opportunities in Lucky Peak State Park, so many visitors go there instead. This lack of visitors keeps Arrowrock an ideal place to engage nature in an active manner. Many of the day-use sites located at Arrowrock Reservoir are only accessible by water, and only one boat launch site exists. Water levels may fall as much as 200 feet when there is heavy water withdrawal for irrigation, but provisions are made for this expected variation at the ramp site. For boaters lucky enough to find it, Arrowrock Reservoir offers excellent water for power boating, water skiing, wake-boarding and sailing. Some swimming is offered at the campsites, most of which are spread along the reservoir and rather primitive. The reservoir lies within the Boise National Forest and is managed by the U.S. Forest Service.

Fishing is one of the most popular activities at Arrowrock Reservoir. Rainbow trout, kokanee, yellow perch, whitefish, and bull trout are all present, but bull trout must be returned to the water as they are a protected species. Some ice fishing can be engaged in away from the main stream of the river. Both the Arrowrock Recreation Area and Boise National Forest are available for hiking, wildlife viewing and hunting in certain areas in season. A number of hiking trails exist in the area, although most are steep and usually termed ‘difficult’. The National Forest provides habitat for bear, deer, mountain goats, quail, pheasant, turkey, grouse, rabbit and a number of other mammals. Mule deer use the area as a part of their annual migration paths. Because of the difficult terrain, the area around Arrowrock Reservoir remains isolated and natural.

Building the dam in the early 1900s was a monumental feat: the process required that the downstream Diversion Dam near Boise be retrofitted with hydroelectric turbines to provide electrical power to the dam site. A railroad was actually constructed to transport materials and workers to the construction location. The dam workforce was treated to such luxuries as electricity, dormitory housing, hot water and a hospital, although they complained about low pay. Provision for future hydroelectric power generation was built into the dam from the beginning, but turbines were not installed until 2010. Because the need for water storage continues to grow, the United States Army Corps of Engineers recently completed a study of the feasibility of adding another 74 feet to the height of the dam – a massive undertaking. The Boise River below the dam forms the farthest reaches of the Lucky Peak Reservoir. Changes to the Arrowrock Dam may well mean changes will occur at Lucky Peak Reservoir also. Environmental concerns will doubtlessly be given heavy weight in any future decision, so it is not likely that any construction will begin in the near future.

Being in such close proximity to the Boise metropolitan area means that the wilderness areas surrounding Arrowrock Reservoir are actually accessible to a large number of people. Named after the river that flows through the city, origins of the city’s name appear to come from the designation of French-Canadian fur trappers in the 1820s who called the river, “La Riviere Boisee”, meaning wooded river. By 1863, the US Army had established a fort in the area to protect parts of the Oregon Trail and silver and gold mining claims in the area – all activities bringing in a large number of settlers. Now a thoroughly modern city and the capital of Idaho, Boise is home to a large number of nature lovers who wish to escape the city and enjoy a day on the water or in the mountains. One of the sport’s hottest new races, the Ironman Boise 70.3 triathlon takes place at Lucky Peak Reservoir for the swimming portion and introduces a new group of athletes to the area every year.

Visitors can enjoy both the best of what Boise has to offer in terms of cultural activities and spend time in solitude on the water within the same afternoon. If visitors choose not to camp at either Arrowrock Reservoir or Lucky Peak State Park next door, a number of small motel lodgings can be found around the area. Rental properties and lodges exist nearby where visitors can enjoy both Arrowrock Reservoir in summer and winter sports during the colder months. Favored activities include cross-country skiing and snowmobiling, with downhill ski venues within a few minutes’ drive. Real estate with mountain or lake views are available in the area, although not at Arrowrock Reservoir. The reservoir and the adjacent recreation area are the ideal spots for cleansing the mind of the clutter of modern living. So come to Arrowrock Reservoir and give your soul a much-needed break. There’s nothing quite like it!

Things to do at Arrowrock Reservoir

  • Vacation Rentals
  • Fishing
  • Ice Fishing
  • Boating
  • Sailing
  • Swimming
  • Water Skiing
  • Camping
  • Hiking
  • Downhill Skiing
  • Cross-Country Skiing
  • Snowmobiling
  • Hunting
  • Wildlife Viewing
  • Birding
  • State Park
  • National Forest

Fish species found at Arrowrock Reservoir

  • Bull Trout
  • Kokanee Salmon
  • Perch
  • Rainbow Trout
  • Trout
  • Whitefish
  • Yellow Perch

Arrowrock Reservoir Photo Gallery

Arrowrock Reservoir Statistics & Helpful Links

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Water Level Control: US Bureau of Reclamation

Surface Area: 3,141 acres

Shoreline Length: 60 miles

Normal Elevation (Full Pond): 3,260 feet

Water Volume: 272,200 acre-feet

Completion Year: 1937

Drainage Area: 2,210 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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