Reservoir report

Puerto-Rico reservoirs & dams

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

Dams in Puerto-Rico

Total storage

330,961ac·ft

High-hazard dams

Updated

May 21

Open the Puerto-Rico reservoir layer on the map Every dam and reservoir filtered to Puerto-Rico on the interactive map.

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May

2026

Reservoir report

Puerto Rico has several major reservoirs and dams that serve as critical sources of water for the island's population and agriculture. The largest reservoir is the Carraízo Lake, which is fed by the Rio Grande de Loíza and other smaller streams. Other major reservoirs include the Dos Bocas and Caonillas Reservoirs. The hydrology of the area is influenced by the central mountain range, which receives the majority of the precipitation and snowpack during the winter months. Drought conditions are common in Puerto Rico, and water conservation measures are often necessary to maintain adequate water supply. In recent years, the island has experienced record drought conditions, with some reservoirs dropping to historic lows. Seasonal trends show that the island's wet season is from May to November, while the dry season runs from December to April. Overall, the management and maintenance of Puerto Rico's reservoirs and dams remain critical to ensuring a reliable water supply for the island's population and agriculture.

Puerto-Rico at a glance

Storage, hazard, and history

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

Hazard classification

High36
Significant0
Low0

USACE downstream-consequence rating, not failure likelihood.

Notable dams

Tallest Cerrillos Dam 323 ft
Oldest Comerio I Dam 1907
Total storage All Puerto-Rico dams 330,961 ac·ft

Built by decade

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

Full inventory

Puerto-Rico dams & reservoirs

Every documented dam in Puerto-Rico. 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.

Name	Year built	Normal storage	Dam height	Max discharge	Hazard	Drainage area
Guajataca Dam	1927	32,600	120	34,600	High	30
Prieto Dam	1955	600	98	32,000	High	10
Lucchetti Dam	1952	14,780	169	62,800	High	17
Loco Dam	1951	1,480	74	24,500	High	8
Guayo Dam	1956	17,400	190	30,200	High	10
Garzas Dam	1943	5,500	201	25,000	High	6
Adjuntas Dam	1950	384	80	37,500	High	15
Pellejas Dam	1950	108	50	22,700	High	9
Dos Bocas Dam	1942	30,420	188	200,000	High	170
Vivi Dam	1950	232	85	25,000	High	7
Caonillas Dam	1948	35,182	235	107,000	High	50
Guineo Dam	1931	1,860	115	7,000	High	2
Guayabal Dam	1913	3,297	130	72,744	High	43
Toa Vaca Dam	1972	55,888	215	77,100	High	22
Matrullas Dam	1934	3,005	120	15,000	High	4
Coamo Dam	1914	100	65	60,000	High	66
La Plata Dam	1974	22,700	131	270,000	High	181
Comerio Ii Dam	1913	600	128	93,000	High	135
Comerio I Dam	1907	500	47	19,970	High	136
Cidra Dam	1946	5,300	115	13,500	High	9
Carite Dam	1913	11,310	104	18,100	High	8
Las Curias Dam	1946	1,120	75	6,400	High	1
Patillas Dam	1976	14,305	127	79,000	High	25
Loiza Dam	1954	23,500	95	312,000	High	207
Yahuecas Dam	1956	1,570	90	38,900	High	17
Ana Mariaâ Ii Dam	1939	373	40	9,862	High	0
Ana Mariaâ V Dam	1939	2,382	53	2,578	High	0
Poncenaâ Dam	1939	1,350	48	·	High	0
Melania Dam	1914	312	30	680	High	1
Ajies Dam Structure 2a	1984	95	52	1,050	High	0
Daguey Dam Structure 3	1978	334	50	2,400	High	1
Lago Regulador	1996	399	39	196	High	·
Fajardo Dam	2002	4,455	115	788	High	0
Rio Â Blanco Dam	2009	3,845	64	·	High	0
Portugues Dam	2015	2,840	220	46,000	High	11
Cerrillos Dam	1992	30,835	323	75,280	High	18

Reservoir FAQ

About Puerto-Rico dams & reservoirs

Where does the Puerto-Rico 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 Puerto-Rico 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 Puerto-Rico have so many dams?

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