(TNS) -- Bobby Lopez first tried calling 911 at about 3 a.m. Sunday.
The floodwaters that had gushed into his parents' Houston garage were rising. The table where his mother, a partially blind and diabetic 60-year-old, sat with Lopez's father and their 3-year-old grandchild would soon be engulfed.
He'd tried driving to them in his truck, but the roads were impassable.
Lopez said he tried calling again, and each time, he was told that dozens of people were ahead in line for help. His parents, too, had dialed 911.
So Lopez did what countless others have done in the wake of a storm that has devastated a region and overwhelmed emergency dispatchers: He took to social media in hopes that someone -- anyone -- would see the plea and come to his family's rescue.
"My mom is stuck in Songwood!" he tweeted, tagging, among others, an unofficial Houston Fire Department rescue account and the Houston Police Department. "Mom elderly and disabled and have my nephew."
As Harvey ripped through the Houston area Saturday night into Sunday, leaving much of the nation's fourth-most populous city under feet of water, scores of residents who had been told to shelter in place were left stranded.
That's when frantic tweets, Facebook messages and videos with captions imploring readers to pass them along began to flood the internet in a kind of improvised emergency dispatch system.
The flooding comes as public agencies around the state grapple with tight budgets and overworked staff. In Dallas, high-profile problems with the city's 911 dispatch system have eroded trust.
Officials like Harris County Sheriff Ed Gonzalez spent the day retweeting messages with the locations of a cancer patient and a pregnant woman in need of transport.
In Dickinson, a photo of nursing home residents waist-deep in murky water was retweeted 207 times. Not much later, 15 seniors were evacuated from the home, according to the Galveston County Daily News.
Dallas County Judge Clay Jenkins, whose office oversees emergency management, said emergency response agencies have a growing array of tools to help them harness social media during a major event.
"We can use word cloud technology to follow what's happening," he said. "A few years ago, we were testing a Salvation Army system [to track tornado damage] and they knew it before the weather stations did."
If residents lose power, they may not have access to the news, but their phones may have battery and cell service.
Of course, Jenkins said, there's always the potential for rumors to find extra life online.
But, ultimately, "I think it's a net positive on helping people."
Still, the catastrophic flooding in Houston may test social media's limits as a way of pinpointing those in most need.
By midday Sunday, the Houston Police Department had put out its own message on various social media channels: Stop using those channels to make formal rescue requests. And don't call 911 asking about flooded roads or power outages.
Lt. Craig Cummings, a spokesman for the Texas Department of Public Safety stationed at the Houston emergency center, said that early on, emergency dispatchers tried to keep track of the requests for help
"For a while, we were doing our best," he said. "We just couldn't do it all."
Instead, he said, the alphabet soup of agencies responding to emergencies were asking residents to call 911 and just wait.
"We have several hundred calls backed up -- they think they're not going to get answered," he said. "If someone has an emergency, they need to call 911 and just know that ... it may take a while to get an answer, but the call takers are working through those calls."
For Lopez, a lifelong Houston resident, "Wait your turn," wasn't good enough when his parents' safety was on the line.
"They took care of you; you're supposed to take care of them," he said.
Eventually, a neighbor with a boat ferried the family to safety.
Lopez's brother contacted another "kid" who was online offering people rides to relatives' homes -- a kid who Lopez described as a "damn angel."
With his parents, brother, nephew now asleep at his house near Lake Houston, the father of three said he hopes to help out however he can. If he comes across any pleas for help online, he said, he'll be sure to retweet.
Staff writer Eline de Bruijn contributed to this report
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