Reservoir report

Hawaii reservoirs & dams

Every documented dam and reservoir in Hawaii — with normal storage capacity, dam height, max discharge, hazard classification, and drainage area. Sourced from USACE NID and state water-resource agencies.

Dams in Hawaii
129
Total storage
35,139ac·ft
High-hazard dams
118
Updated
May 24
Open the Hawaii reservoir layer on the map Every dam and reservoir filtered to Hawaii on the interactive map.
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May
24
2026
Reservoir report
Hawaii has several reservoirs and dams that provide water for irrigation, hydroelectric power generation, and domestic use. The largest reservoirs in the state are Wahiawa and Kealia, which are located on the islands of Oahu and Kauai, respectively. Both reservoirs are fed by streams that originate in the mountainous regions of the islands, and they can hold up to tens of billions of gallons of water.

Snowpack is not a significant factor in Hawaii's hydrology, as the state is located in a tropical region and does not experience significant snowfall. Instead, rainfall is the primary source of water for the reservoirs and rivers in Hawaii.

Drought conditions can be a concern in Hawaii, particularly during El Niño years when rainfall is reduced. In 2016, Hawaii experienced a severe drought that affected agricultural production and led to water restrictions.

Overall, the hydrology of Hawaii is closely tied to its mountainous topography and tropical climate, with rainfall and streamflow playing a critical role in the availability of water for the state's residents and industries.
Hawaii at a glance

Storage, hazard, and history

How the Hawaii dam inventory breaks down -- aggregate stats computed across every documented dam in the state.

Hazard classification

  • High118
  • Significant4
  • Low7

USACE downstream-consequence rating, not failure likelihood.

Notable dams

  • Tallest Alexander 112 ft
  • Oldest Kaupakalua Reservoir 1885
  • Total storage All Hawaii dams 35,139 ac·ft

Built by decade

Most U.S. dams were built mid-20th century during the federal water-development era.

Full inventory

Hawaii dams & reservoirs

Every documented dam in Hawaii. Sortable by any column; quickly filterable by name. Numeric columns heat-mapped from light to deep based on value. Tap any dam for the full report.

129 dams
Name Year built Normal storage Dam height Max discharge Hazard Drainage area
Nuuanu Dam No. 4 1910 242 66 4,000 High 1
Puu Lua Reservoir 1925 844 105 · Significant 0
Puu Opae Reservoir 1930 193 41 · Low ·
Kitano Reservoir (Removed) 1928 110 38 · High 0
Mana Reservoir 1905 135 17 · High 0
Waikaia Reservoir 1951 44 26 · High 0
Kepani Reservoir 1954 72 32 · High 0
Waikoloi Reservoir 1958 130 64 · High 0
Kaawanui Reservoir 1950 83 26 200 High 0
Waiakalua Reservoir 1920 184 26 · High 0
Aii Reservoir 1920 68 21 · High 0
Kapaia Reservoir 1910 1,105 50 · High 3
Upper Kapahi Reservoir (Reduced) 1910 94 40 515 High 0
Okinawa Reservoir 1920 84 25 1,000 High 1
Kaneha Reservoir 1910 356 46 · High 1
Mimino Reservoir 1920 51 44 · High 0
Wahiawa Dam 1906 7,761 88 24,500 High 17
Opaeula 01 Reservoir 1910 186 66 0 High 0
Kemoo 5 Reservoir 1920 63 21 167 High 0
Upper Helemano Reservoir 1912 479 46 0 High 0
Helemano 6 Reservoir 1915 66 36 0 High 1
Kalihiwai Reservoir 1920 278 20 · High 0
Ku Tree Reservoir 1925 880 90 5,600 High 1
Kaloko Reservoir 1890 1,255 27 · High 0
Waikoloa Reservoir No. 1 1970 157 44 160 High ·
Kualapuu Reservoir 1969 4,265 57 700 High 0
Waimea 60 Mg Reservoir 1957 176 50 · High 0
Puukapu Watershed Retarding Dam R-1 1965 · 12 2,000 High 3
Waikamoi Dam No. 2 1956 32 34 · Low 2
Piiholo 50 Mg Reservoir 1971 162 42 · High 0
Olinda Reservoir 1918 26 42 · High 0
Keaiwa Reservoir 1920 42 32 81 Low 0
Hawi No. 5 Reservoir 1930 55 20 · High ·
Horner Reservoir 1926 71 70 34 High 0
Hanakaoo Reservoir 1918 25 27 7 High 0
Kahoma Reservoir 1918 18 60 77 High 0
Honokowai Reservoir 1918 10 31 · High 0
Reservoir 140 1926 43 35 340 High 0
Wailua Reservoir 1920 757 40 · High 1
Lower Kapahi Reservoir 1920 144 20 · High 0
Twin Reservoirs 1920 162 18 1,800 High 0
Aahoaka Reservoir 1910 164 36 · High 1
Upper Anahola Reservoir 1920 83 27 · Low 0
Field 1 Kealia Reservoir 1920 80 29 · High 0
Maui Reservoir 14 1913 21 30 · High 0
Maui Reservoir 15 1917 17 39 · High 1
Maui Reservoir 20 1913 150 42 72 High 0
Maui Reservoir 21 1913 57 22 175 High 0
Maui Reservoir 22 1917 135 30 610 High 0
Maui Reservoir 24 1917 46 39 100 High 3
Maui Reservoir 25 1917 123 20 · High 0
Maui Reservoir 30 1917 65 23 · High 0
Maui Reservoir 33 1910 143 30 · High 0
Maui Reservoir 40 1926 159 42 · High 0
Maui Reservoir 42 1917 32 27 · High 0
Maui Reservoir 52 1917 227 13 · High 0
Maui Reservoir 60 1917 247 25 · High 0
Maui Reservoir 61 1917 163 20 · High 0
Maui Reservoir 70 1917 59 16 · High 0
Maui Reservoir 73 1908 205 25 3,500 High 1
Maui Reservoir 74 1916 106 25 2,000 High 1
Maui Reservoir 80 1917 126 27 · High 0
Maui Reservoir 81 1920 115 19 · High 0
Maui Reservoir 82 1917 55 13 · Significant 0
Maui Reservoir 84 1918 108 29 · High 1
Maui Reservoir 90 1917 138 13 · High 1
Maui Reservoir 92 1967 52 16 · High 0
Peahi Reservoir 1924 66 35 · High 1
Papaaea Reservoir 1902 130 37 31 High 0
Kaupakalua Reservoir 1885 190 57 · High 3
Kapalaalaea Reservoir 1885 153 48 · High 1
Haiku Reservoir 1904 178 37 · High 1
Pauwela Reservoir 1904 98 47 590 High 1
Alexander 1931 1,070 112 621 High 3
Waita Reservoir 1906 3,400 23 2,000 High 3
Kapa Reservoir 1901 26 21 · High 0
Hukiwai Reservoir 1910 50 33 · Low 0
Ioleau Reservoir 1902 107 48 · Low 0
Aepo Reservoir 1901 381 70 600 High 0
Huinawai Reservoir 1902 145 48 680 High 0
Elima Reservoir 1901 91 38 567 High 0
Kumano Reservoir 1902 150 48 · High 0
Puu O Hewa Reservoir 1915 73 23 320 High 0
Kaupale Reservoir 1910 222 49 · High 0
Ipuolono Reservoir 1910 415 45 · High 2
Aepoalua Reservoir 1915 124 33 70 High 0
Aepoekolu Reservoir 1910 134 37 2,475 High 0
Aepoeha Reservoir 1913 554 42 · High 1
Omao Reservoir 1915 139 40 3,000 High 1
Piwai Reservoir 1916 222 56 487 High 0
Pia Mill Reservoir 1910 31 17 440 High 0
Mau Reservoir 1901 67 38 · High 0
Elua Reservoir 1902 246 30 4,700 High 1
Manuhonuhonu Reservoir 1954 41 45 · High 0
Mauka Reservoir 1910 110 19 2,193 High 1
Papuaa Reservoir 1914 · 43 · High 2
Halenanahu Reservoir 1920 460 35 · High 1
Waikoloa Reservoir No. 2 1975 157 31 250 High 0
Puu Pulehu Reservoir 1910 338 20 93 High 1
Kaneohe Dam 1980 260 83 15,000 High 2
Kahana Nui Dam 1984 59 49 25,884 High 5
Napili 4-5 Desilting Basin 1985 0 14 1,600 High 1
Napili 2-3 Desilting Basin 1988 17 39 1,030 High 0
Waimanalo 60 Mg Reservoir 1993 182 65 200 High 0
Honokowai - Structure #8 1995 79 41 38,147 High 6
Paauilo Reservoir 1975 35 34 100 Significant 0
Upper Field 14 Reservoir 1985 17 38 100 High 0
Puu Koa Reservoir 1985 16 37 90 High 0
Kaopala Basin 1998 · 30 7,200 High 1
Waikoloa Reservoir No. 3 1985 153 54 · High 0
Oahu Reservoir 155 1916 · 25 110 High 0
Kahakapao Reservoirs 1990 · 54 · High 0
Maui Field 290 Reservoir 1997 11 25 90 High 0
Ukumehame Reservoirs · 35 29 · High 4
Kehalani Offsite Retention Basin 2003 · 30 2,076 High 1
Middle Field 14 Reservoir 2006 13 36 · High 0
Kaili Ili Reservoir 1984 25 25 · High 0
Mahinahina Reservoir 1995 61 34 31 High 0
Kauai Lagoons 1987 395 15 · High 1
Halaula Reservoir · · 26 · High 0
Punawai Reservoir 1970 29 38 · High 0
Maunaolu Reservoir 1966 18 27 · High ·
Wailuku Water Reservoir 6 · 35 33 · High 0
Wailuku Water Reservoir 10 · 40 52 · High 0
Waikamoi Reservoirs 1980 92 20 · Significant 0
Plantation Reservoir 1989 24 31 · High 0
Nuuanu Reservoir No. 1 1905 44 34 428 High 0
Pond No. 1 At Kauai Ranch 2004 26 32 · High 0
Koolau Reservoir 1919 122 70 · Low 0
Reservoir FAQ

About Hawaii dams & reservoirs

Where does the Hawaii dam data come from?

The U.S. Army Corps of Engineers National Inventory of Dams (NID) plus state water-resource agencies. Snoflo joins these public records with live USGS streamgauge readings downstream where available. The NID is the canonical federal dam registry.

What does Hazard Potential mean?

USACE classifies every dam by what would happen if it failed: Low (no loss of life expected, minimal economic damage), Significant (no loss of life but economic, environmental, or lifeline damage), High (loss of life expected). It's a downstream-consequence rating, not a likelihood of failure.

What is Normal Storage in acre-feet?

The volume of water the reservoir holds at its normal operating level, measured in acre-feet. One acre-foot is about 325,851 gallons or 1,233 cubic meters — the amount needed to cover one acre to a depth of one foot.

Why are some Hawaii dams missing storage or height data?

USACE NID records can have gaps for small or older dams that pre-date federal reporting requirements. Snoflo surfaces whatever the canonical record contains. If a dam you care about has incomplete data, contact the operating agency or USACE for updates.

Can I see live water levels?

Yes — tap any dam name to open its detail page, which pulls live storage data from USGS streamgauges or operating-agency feeds where available. Historical levels and seasonal averages are also shown.

Why does Hawaii have so many dams?

The U.S. has over 90,000 dams — most built between 1930 and 1980 during the federal water-development era. Hawaii's count reflects a combination of agricultural irrigation needs, flood control, hydropower, and recreation. The "Built by decade" chart above shows the timeline.

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