When Joe Garcia spotted a rescue boat on Monday outside his flooded home in Spring, a suburb north of Houston, he pushed a plastic tub of his belongings through chest-high water and loaded it on the boat. Then he returned to his home to grab one more prized possession: Heidi, his German shepherd.

Garcia, his body soaked, carried Heidi through the rising floodwaters, making sure her head stayed dry, and lifted her to safety on a volunteer’s fishing boat. They were whisked away in a moment captured by a photographer with The Associated Press.

Over the past several days, Tropical Storm Harvey has unleashed breath-taking amounts of rain in the Houston area, paralysing the region and transforming streets into fast-moving rivers. Thousands of people have been displaced, with many still waiting to be rescued.

When people are plucked to safety, they often take with them the clothes on their backs and the few possessions they can carry. For many people, that includes taking their pets, hoisting them onto boats and into high-water vehicles before riding together to dry ground.

But that is not always the case. Many pets have been left behind, abandoned in homes, chained to trees and left for strangers and animal shelters to round up and rescue. And some animals such as cattle were simply too big to move before Harvey arrived.

But Winston and Baxter, a West Highland terrier and a Shih Tzu, were never going to leave Belinda Penn’s side. The floodwaters began to seep through the exterior doors of her home in Spring on Sunday afternoon and started to fill up the first floor.

She and her husband, Scott, grabbed the dogs and retreated to their second floor. The family was upended, but Winston and Baxter had their crates and food on the second floor. It did not matter, though, Belinda Penn said. They were too nervous to eat.

Around 11am on Monday, a neighbour told the Penns that a rescue boat was on the way. They loaded garbage bags with clothes and dog food, and carried the dogs through the water. On Monday night, they had reached Belinda Penn’s mother’s apartment in the suburb of The Woodlands.

“Every situation is different, but for us, it was not an option to leave our pets behind,” Penn said. “They are my best friends.”

Other animals were not as fortunate.

A woman in Corpus Christi said on Twitter that she took in her neighbour’s dog left in the backyard. A photographer for The Daily Mail rescued a dog he found chained to a pole in Victoria, waters rising around him, the paper reported. In Dickinson, a CNN reporter spotted two retrievers abandoned in a boat.

In San Antonio, the city’s Animal Care Services Department had taken in about 200 displaced animals as of Monday afternoon. More were on the way.

Rescued dogs were being held in rows of cages in an air-conditioned warehouse east of downtown San Antonio. Cats, for their own peace of mind, were taken to a separate location.

“Our commitment is for as long as it takes and as long as the nation needs our help,” Heber Lefgren, the department’s director, said in an interview.

Some animals already in the shelter’s care before the storm were expected to be flown to animal centres in other states to make room for pets displaced by Harvey. On Tuesday morning, the first flight full of dogs and cats is scheduled to depart San Antonio for New Jersey. On Wednesday, a flight will head to Seattle.

“There’s a likelihood that this could go on for weeks, because as the waters recede, they are going to be finding more and more pets that are displaced,” said Kim Alboum, a director at the Humane Society of the United States, which was organising the flights.

Pets were also helping rescuers track down people who were stuck in their homes. On Monday, Marty Lancton and another firefighter in Houston were driving people to rescue in a boat in southwestern Houston when he spotted two dogs on a roof.

“Something didn’t sit right,” Lancton said, describing why it caught his attention.

The firefighters, their boat already crowded as they ran rescues, pulled closer to the home and soon saw a message on the glass of the front door: “Help.”

“We backed up the boat — the water was almost halfway to three-quarters of the way up the house — we busted the window, tried to call for somebody and the homeowner was in the garage,” said Lancton, the President of the Houston Professional Fire Fighters Association.

The aftermath of Hurricane Harvey Show all 19 1 /19 The aftermath of Hurricane Harvey The aftermath of Hurricane Harvey A tattered U.S. flag damaged in Hurricane Harvey, flies in Conroe, Texas Reuters The aftermath of Hurricane Harvey Lisa Rehr holds her four-year old son Maximus, after they lost their home to Hurricane Harvey, as they await to be evacuated with their belongings from Rockport, Texas Reuters The aftermath of Hurricane Harvey People line up for food as others rest at the George R. Brown Convention Center AP Photo/LM Otero The aftermath of Hurricane Harvey Volunteers with The American Red Cross register evacuees at the George R. Brown Convention Center Reuters/Nick Oxford The aftermath of Hurricane Harvey Soldiers with the Texas Army National Guard help the residents of Cyprus Creek Reuters The aftermath of Hurricane Harvey Residents wade through floodwater Reuters/Nick Oxford The aftermath of Hurricane Harvey Residents walk along the flooded roadway of Texas 249 as they evacuate their adjacent neighborhoods EPA The aftermath of Hurricane Harvey A man floats past a truck submerged on a freeway flooded by Tropical Storm Harvey on Sunday AP The aftermath of Hurricane Harvey People are rescued by airboat as they evacuate from flood waters from Hurricane Harvey in Dickinson, Texas Reuters The aftermath of Hurricane Harvey James Archiable carries his bike through the flooded intersection at Taylor and Usenet near downtown Houston, Texas EPA The aftermath of Hurricane Harvey A massive sinkhole opened up on a motorway in Rosenburg, a city 25 miles southwest of Houston, Texas Rosenberg Police The aftermath of Hurricane Harvey People are rescued from flood waters from Hurricane Harvey in an armored police mine-resistant ambush protected vehicle in Dickinson, Texas Reuters The aftermath of Hurricane Harvey People are rescued from flood waters from Hurricane Harvey on a boat in Dickinson, Texas Reuters The aftermath of Hurricane Harvey Evacuees are airlifted in a US Coast Guard helicopter after flooding due to Hurricane Harvey inundated neighborhoods in Houston, Texas Reuters The aftermath of Hurricane Harvey Evacuees leave a US Coast Guard helicopter after being rescued from flooding due to Hurricane Harvey in Houston, Texas Reuters The aftermath of Hurricane Harvey Residents look on at a submerged motorway during a break in the rain in Houston, Texas EPA The aftermath of Hurricane Harvey People photograph the submerged motorway interchange EPA The aftermath of Hurricane Harvey Debris lies on the ground after a building was destroyed by Hurricane Harvey in Aransas Pass, Texas AP The aftermath of Hurricane Harvey Dominic Dominguez searches for his boat in a boat storage facility that was heavily damaged by Hurricane Harvey near Rockport, Texas EPA

He said he never found out why the dogs were put on the roof. Maybe there was no room in the house. Maybe they were there to catch someone’s attention.

“Either way, it worked,” Lancton said.