The catastrophic flooding in Houston and its surroundings has put strain on communication networks and brought about network outages.

As the storm took hold at the start of the weekend, cell carriers including Verizon, AT&T, and Sprint offered customers affected by tropical storm Harvey free calls, text messages, and data. But, as TechCrunch notes, call volumes and a lack of options for recharging cell phones meant that the offer wasn’t a whole lot of use. In fact, many people couldn’t get through to the U.S. Coast Guard to report their need for help, and emergency services declined to take calls via social media.

To top it off, the Wall Street Journal says some areas suffered almost total telecom outages as a result of infrastructure damage caused by flooding and high winds. As of Sunday, some regions, such as Rockport, Texas, had as many as 95 percent of cell towers out of action. The Federal Communications Commission also told the newspaper that 148,565 people were left without wired connections in the region. It’s thought that many of the outages won’t be rectified until roads are deemed safe enough for technicians to travel.

Ensuring that communication links stay up during times of natural disaster is difficult, but some firms have been trying to develop systems that use local Wi-Fi and Bluetooth connections on smartphones to transfer data even when networks are down. Earlier this year, for instance, we reported that the Weather Company had developed an app that could provide emergency alerts about extreme weather and natural disasters using a technique known as mesh networking.