The Affordable Care Act’s health insurance co-ops absorbed deep financial losses last year, and 2016 is shaping up to be a make-or-break year for these nonprofit alternatives to traditional insurers.

Officially called Consumer Operated and Oriented Plans, these still-fledgling insurers were devised during the ACA’s creation to inject competition into insurance markets. But they have struggled from the start to build a customer base from scratch and deal with higher-than-expected expenses, among other problems.

Heading into their third full year of operation, the co-ops are adding customers and improving their coverage, but they also face the end of some government programs designed to support insurers as they build business on the ACA’s public insurance exchanges. They will have to determine soon whether their businesses can stand on their own and compete with more established carriers.

“Plan year 2016 is a critical year for these co-ops — they must move from startup to stability and improve their financial capabilities,” said Kevin Counihan, CEO of the federal exchange operator HealthCare.gov, during a Thursday hearing held by the Senate’s Homeland Security & Government Affairs Committee.

A dozen of the 23 co-ops created under the law have closed, and many of the survivors lost well over $20 million last year, according to recently filed annual statements compiled by the National Association of Insurance Commissioners.

But the co-ops also hit a growth spurt and now cover more than 350,000 people, or nearly triple their total from 2014. Enrollment is growing better than expected and patient populations appear to be getting younger and healthier in some cases. That can help cut future expenses.

Plus, the co-ops are learning more about their patient population, which can help them price future coverage to cover claims.

These insurers knew 2015 would be ugly, according to Kelly Crowe, CEO of the trade association the National Alliance of State Health Co-Ops. But she said last year’s numbers don’t reflect where the co-ops stand today. Crowe noted that many are growing methodically and adding more stable, employer-sponsored coverage.

“We’re optimistic that they will continue to grow and be a viable alternative for people in selecting their health care,” she said. “They are still financially fragile, though. There obviously is still some risk there, as there is with any start up business.”

Maryland’s Evergreen Health Cooperative did the best of the remaining co-ops in 2015, booking a loss of $10.8 million. Land of Lincoln Mutual Health Insurance Co. in Illinois lost $90.8 million.

Maine’s Community Health Options made $7.3 million in 2014 but lost $74 million last year. More than half of that stemmed from a reserve the insurer set aside to cover future losses.