A plantain field stands under water after the passing of Hurricane Maria in Yabucoa, Puerto Rico, Thursday, September 21, 2017. As of Thursday evening, Maria was moving off the northern coast of the Dominican Republic with winds of 120 mph (195 kph). The storm was expected to approach the Turks and Caicos Islands and the Bahamas late Thursday and early Friday.
Carlos Giusti/AP
A plantain field stands under water after the passing of Hurricane Maria in Yabucoa, Puerto Rico, Thursday, September 21, 2017. As of Thursday evening, Maria was moving off the northern coast of the Dominican Republic with winds of 120 mph (195 kph). The storm was expected to approach the Turks and Caicos Islands and the Bahamas late Thursday and early Friday.
Now playing
01:28
Imminent dam break triggers mass evacuations
Stacks upon stacks of bottled water sit near a runway in Ceiba, Puerto Rico, on September 12, 2018.
Julian Quiñones/CNN
Stacks upon stacks of bottled water sit near a runway in Ceiba, Puerto Rico, on September 12, 2018.
Now playing
02:42
See untouched water bottles in Puerto Rico
SAN ISIDRO, PUERTO RICO - OCTOBER 15:  Uncollected debris stand near damaged homes in an area without electricity on October 15, 2017 in San Isidro, Puerto Rico. Puerto Rico is suffering shortages of food and water in many areas and only 15 percent of grid electricity has been restored. Puerto Rico experienced widespread damage including most of the electrical, gas and water grid as well as agriculture after Hurricane Maria, a category 4 hurricane, swept through.  (Photo by Mario Tama/Getty Images)
Mario Tama/Getty Images South America/Getty Images
SAN ISIDRO, PUERTO RICO - OCTOBER 15: Uncollected debris stand near damaged homes in an area without electricity on October 15, 2017 in San Isidro, Puerto Rico. Puerto Rico is suffering shortages of food and water in many areas and only 15 percent of grid electricity has been restored. Puerto Rico experienced widespread damage including most of the electrical, gas and water grid as well as agriculture after Hurricane Maria, a category 4 hurricane, swept through. (Photo by Mario Tama/Getty Images)
Now playing
01:39
Puerto Rico revises Hurricane Maria death toll
title:  duration: 00:00:00 site:  author:  published:  intervention: yes description: Radio Isla had access to vans that contained water, food, medicine and hundreds of open boxes, many of them with reptile waste and in a state of decomposition. According to sources, the supplies were for the victims of the hurricanes.
Radio Isla
title: duration: 00:00:00 site: author: published: intervention: yes description: Radio Isla had access to vans that contained water, food, medicine and hundreds of open boxes, many of them with reptile waste and in a state of decomposition. According to sources, the supplies were for the victims of the hurricanes.
Now playing
01:24
Supplies sent to Puerto Rico found abandoned
MOROVIS, PUERTO RICO - DECEMBER 20:  A resident, whose home remains without electricity, watches as debris is removed on December 20, 2017 in Morovis, Puerto Rico. Barely three months after Hurricane Maria made landfall, approximately one-third of the devastated island is still without electricity and 14 percent lack running water. While the official death toll from the massive storm remains at 64, The New York Times recently reported the actual toll for the storm and its aftermath likely stands at more than 1,000. Puerto Rico's governor has ordered a review and recount as the holiday season approaches.  (Photo by Mario Tama/Getty Images)
Mario Tama/Getty Images/File
MOROVIS, PUERTO RICO - DECEMBER 20: A resident, whose home remains without electricity, watches as debris is removed on December 20, 2017 in Morovis, Puerto Rico. Barely three months after Hurricane Maria made landfall, approximately one-third of the devastated island is still without electricity and 14 percent lack running water. While the official death toll from the massive storm remains at 64, The New York Times recently reported the actual toll for the storm and its aftermath likely stands at more than 1,000. Puerto Rico's governor has ordered a review and recount as the holiday season approaches. (Photo by Mario Tama/Getty Images)
Now playing
01:47
Possible epidemic in Puerto Rico after Maria hit
CNN
Now playing
02:04
Suspected deadly bacteria cases in Puerto Rico (2017)
With hurricane season starting June 1, CNN returns to Puerto Rico to see if the island is ready for another storm. Nine months after Maria, 20,000 homes are still without power- and going into the season, many mayors are worried that even a small storm will plunge them back into darkness and repeat the crisis all over again. We witness desperate Puerto Ricans illegally and dangerously turning on their own power, and press officials for answers on what will change this time around.
CNN
With hurricane season starting June 1, CNN returns to Puerto Rico to see if the island is ready for another storm. Nine months after Maria, 20,000 homes are still without power- and going into the season, many mayors are worried that even a small storm will plunge them back into darkness and repeat the crisis all over again. We witness desperate Puerto Ricans illegally and dangerously turning on their own power, and press officials for answers on what will change this time around.
Now playing
01:05
Questions surround Hurricane Maria death toll
Guest: Mayor Carmen Cruz from San Juan, PR (Facetime) Anderson in Studio 73 / Control 71 (channel 67)   Please record CTL 7100 Switched Please record CTL 7103 Clean Switched Please record CTL 7138 AC ISO Please record CTL 7139 Splits Please record CTL 7140 Big Smalls Please record GFX 905 Cruz ISO
CNN
Guest: Mayor Carmen Cruz from San Juan, PR (Facetime) Anderson in Studio 73 / Control 71 (channel 67) Please record CTL 7100 Switched Please record CTL 7103 Clean Switched Please record CTL 7138 AC ISO Please record CTL 7139 Splits Please record CTL 7140 Big Smalls Please record GFX 905 Cruz ISO
Now playing
01:59
San Juan mayor: Trump showed terrible neglect
CNN
Now playing
01:58
CNN anchor presses PR governor on death count
SAN ISIDRO, PUERTO RICO - OCTOBER 05:  Kids bike in an area without grid power or running water about two weeks after Hurricane Maria swept through the island on October 5, 2017 in San Isidro, Puerto Rico. Puerto Rico experienced widespread damage including most of the electrical, gas and water grid as well as agriculture after Hurricane Maria, a category 4 hurricane, swept through.  (Photo by Mario Tama/Getty Images)
Mario Tama/Getty Images
SAN ISIDRO, PUERTO RICO - OCTOBER 05: Kids bike in an area without grid power or running water about two weeks after Hurricane Maria swept through the island on October 5, 2017 in San Isidro, Puerto Rico. Puerto Rico experienced widespread damage including most of the electrical, gas and water grid as well as agriculture after Hurricane Maria, a category 4 hurricane, swept through. (Photo by Mario Tama/Getty Images)
Now playing
03:36
Puerto Ricans repair power lines themselves
ricardo rossello
CNN
ricardo rossello
Now playing
02:13
Rossello: Hell to pay if data not available
MOROVIS, PUERTO RICO - DECEMBER 20:  A resident, whose home remains without electricity, watches as debris is removed on December 20, 2017 in Morovis, Puerto Rico. Barely three months after Hurricane Maria made landfall, approximately one-third of the devastated island is still without electricity and 14 percent lack running water. While the official death toll from the massive storm remains at 64, The New York Times recently reported the actual toll for the storm and its aftermath likely stands at more than 1,000. Puerto Rico's governor has ordered a review and recount as the holiday season approaches.  (Photo by Mario Tama/Getty Images)
Mario Tama/Getty Images/File
MOROVIS, PUERTO RICO - DECEMBER 20: A resident, whose home remains without electricity, watches as debris is removed on December 20, 2017 in Morovis, Puerto Rico. Barely three months after Hurricane Maria made landfall, approximately one-third of the devastated island is still without electricity and 14 percent lack running water. While the official death toll from the massive storm remains at 64, The New York Times recently reported the actual toll for the storm and its aftermath likely stands at more than 1,000. Puerto Rico's governor has ordered a review and recount as the holiday season approaches. (Photo by Mario Tama/Getty Images)
Now playing
02:20
Study: Puerto Rico hurricane death toll near 5,000
A Puerto Rico Electric and Power Authority brigade work in a remote off-road location to repair a downed power transmission line in Ponce, Puerto Rico on November 29, 2017. / AFP PHOTO / Ricardo ARDUENGO / TO GO WITH AFP STORY By Leila MACOR, US-PuertoRico-power-weather-reconstruction-hurricane        (Photo credit should read RICARDO ARDUENGO/AFP/Getty Images)
RICARDO ARDUENGO/AFP/Getty Images/FILE
A Puerto Rico Electric and Power Authority brigade work in a remote off-road location to repair a downed power transmission line in Ponce, Puerto Rico on November 29, 2017. / AFP PHOTO / Ricardo ARDUENGO / TO GO WITH AFP STORY By Leila MACOR, US-PuertoRico-power-weather-reconstruction-hurricane (Photo credit should read RICARDO ARDUENGO/AFP/Getty Images)
Now playing
01:20
Puerto Rico suffers island-wide power outage
Blue tarps are still the only roofs for some homes in Corozal.
Leyla Santiago/CNN
Blue tarps are still the only roofs for some homes in Corozal.
Now playing
02:46
Puerto Rico 6 months after Hurricane Maria
CNN
Now playing
03:47
Deaths in PR still attributed to Maria
CNN
Now playing
03:45
Hurricane Maria evacuees living in FL motels
CNN —  

All people living near the Guajataca River in northwest Puerto Rico should evacuate immediately because of an “imminent dam break,” the National Weather Service in San Juan said Friday afternoon.

“All Areas surrounding the Guajataca River should evacuate NOW. Their lives are in DANGER! Please SHARE!” an earlier tweet said.

About 70,000 people in the area of the Guajataca Dam have been told to evacuate, National Guard spokeswoman Yennifer Alvarez told CNN’s Leyla Santiago. Buses have been brought in to help people leave.

Puerto Rico Gov. Ricardo Rossello said on Saturday afternoon that the dam was holding up, but residents should still evacuate the area until further notice.

“We don’t know how much longer it will hold,” said Rossello. “The structure has been significantly compromised.”

Due to damaged telephone lines and lack of radio contact, Rossello said authorities have to physically go to the area and alert residents of the dangers posed by a possible dam breach.

Speaking on CNN’s “Out Front” with Erin Burnett, Puerto Rican Secretary of State Luis Gerardo Rivera Marín said the evacuations are difficult because the island was heavily damaged by Hurricane Maria, which struck earlier this week. Many parts of Puerto Rico are flooded and more than 3 million people don’t have electricity.

“It is (done) in the blackness of the night,” he said. “There’s lack of energy, especially in the mountain regions where the winds were higher speeds.”

Google Earth image of the Guajataca Dam in Puerto Rico.
Google Earth
Google Earth image of the Guajataca Dam in Puerto Rico.

The NWS issued a flash-flood notice for the towns of Isabela and Quebradillas, which are about 6 miles apart. Isabela has about 45,000 people, Quebradillas 25,000 people.

The dam was constructed by the Puerto Rico Electric Power Authority to create a lake that provides drinking water to residents of the area, according to the US Geological Survey.

CNN’s Gisela Crespo in Atlanta contributed to this report.