Less than a year after dockless bike-share systems arrived in the District, the colorful bikes are being stolen and vandalized in growing numbers, with one city official saying that some companies have lost up to 50 percent of their fleets.

The companies acknowledge that some users have figured out how to cheat their systems, such as using prepaid credit cards or taking bicycles that haven’t been properly locked by paying riders, but they contend the losses are not as high as 50 percent. Some of the companies say they are taking extra measures to improve their locking and GPS tracking systems.

“They have lost a lot of their bikes,” Kimberly Lucas, the city’s bike program specialist told a group of regional transportation officials at a dockless-bike-share workshop sponsored by the Metropolitan Washington Council of Governments in May. She said companies have told city transportation officials that they have lost up to half of their fleets, which is significant because each company is allowed to operate a maximum of 400 bikes in the city.

“They are being left unlocked, and somebody wants it, they need it, they take it, they drop it off, and they are just not ending the trip because they maybe weren’t required to put in a credit card on file,” Lucas told the group.

District officials declined to make Lucas available for an interview. A city spokesman said he companies have reported a combined 326 bikes missing or vandalized.

Theft and vandalism of the bikes, which rent for as little as $1 a ride, have been problems in other cities in the United States and around the world, where dockless operations have grown exponentially in the last year.  In the District, one of the first U.S. cities to experiment with the dockless model, bikes have been found dismantled, dumped in creeks and abandoned along highways.

In Europe, the dockless firm Gobee.bike was forced to abandon operations in Paris after thousands of its bikes were stolen and destroyed. It also stopped operating in Brussels and Rome because of significant vandalism to its fleet.

In the United States, reports of vandalism have poured out on social media, and officials have denounced sightings of bikes left destroyed and at crime scenes. In Seattle, where there are as many as 7,000 dockless bikes from three vendors, city officials say they have had incidents in which people have cut the wires of the bikes, not only destroying the bikes but also posing a safety hazard for riders unaware of the bikes’ damaged condition.

In Arizona, a pile of dozens — if not hundreds — of LimeBike bikes was spotted last week at a scrapyard just northwest of Phoenix. A company spokesman said the bikes “were damaged beyond repair” and were being recycled.

LimeBike has been operating in the United States for about a year.

In addition to LimeBike, the companies participating in the District’s dockless program are Mobike, Spin, Ofo and  Jump. Limebike also has scooters in its fleet. Two other companies, Bird and Skip (formerly Waybots), operate scooters only.

The operators declined to provide specific data on their losses. They said theft and vandalism were common in the early months of operations but have dropped significantly since then. Because the bikes are equipped with GPS, the recovery rate is high, they said.

“Fifty percent is extremely high,” said Euwyn Poon, co-founder and president of Spin, which plans to add scooters to its fleet. “We don’t really experience bikes going missing or being vandalized in D.C. or in other parts of the country.

“Initially, when the service was brand new, there was some loss and vandalism. When you have a product that’s available for public consumption, you account for that,” Poon said. “However, that has decreased dramatically as bike-share has become more ingrained in the public infrastructure.”

The companies have been operating in the city since a pilot program launched in September. The pilot was scheduled to end in April but was extended to the end of August. City officials are expected to come up with a plan for a permanent program during this testing period and are evaluating how the bike services are performing, including problems with theft and vandalism.

Some companies say promotions in the early days of the program may have led to problems. For example, riders taking advantage of free rides weren’t securely locking the bikes after completing a trip. Thieves are then able to use the unlocked bicycles to take rides without using a credit card. Some companies say they now offer incentives for customers to properly lock the bikes.

City transportation officials say the pilot’s cap on the number of bikes is essentially to limit bike litter. But as part of the pilot, they are assessing whether demand exists to raise the limit or eliminate it. The companies say 400 bikes are not enough to make a profit and deploy them to all four quadrants of the city as required.

To prevent thefts, China-based Ofo is exploring technology enhancements and applying penalties for users who fail to lock their bike, spokesman Jordan Levine said.

Mary Caroline Pruitt, a spokeswoman for LimeBike, said the company takes “meaningful steps” to prevent vandalism and theft.

“All our bikes and scooters have anti-theft locks and audible alarms that sound if someone tries to tamper with them,” she said. “If we find someone has vandalized one of our products, we do our best to make sure they are held responsible, including working with local authorities when appropriate.”

Jump bikes, owned by Uber, incorporates theft-resistant features, including protected and integrated screws and cables, a spokesman said.

“We’ve lost less than 1 percent of our fleet to theft and vandalism in [the] first 6 months of operation in D.C.,” a Jump spokesman said. Jump bikes have an integrated U-lock and the company requires users to lock the bike to a bike rack or other existing infrastructure to prevent bike litter, a feature that also contributes significantly to reducing bike theft, the spokesman said.

“We know the location, battery status and mechanical status of our entire fleet at all times,” the spokesman said.

Lucas, the city transportation official, said the No. 1 thing that would limit theft is requiring a credit card for rental; however, being able to rent the bikes without a credit card is also what makes the systems more accessible to a more diverse group of users.

“They are making them more accessible in a lot of ways,” she said. But she said, the theft problem presents challenges for the city as it evaluates the effectiveness of the systems.

“How do we know that they only have 400 bikes operating in the jurisdiction?” she said. “… Is that 400 bikes including 200 that were stolen? Or that 400 bikes that they say that are in operations and another 200 were stolen, so really there are 600 bikes floating around? These are part of the things that we are looking at in this evaluation program,” she said.