Federal officials said they've rescued more than 940 sea lion pups along the California coast since the first of the year.
All those rescues are putting a strain on wildlife rescue organizations.
About 220 sea lion pups are typically in need of rescue during the first four months of the year. This year's total is already four times that average.
This is the second time in three years that there's been a major incident linked to sea lion health.
Researchers recently visited the sea lions' Channel Islands breeding grounds and on Wednesday discussed their findings.
The situation will likely get worse before it gets better, said Justin Viezbicke of the National Oceanic and Atmospheric Administration.
"Most of our facilities are either at capacity, or getting close to it. We're at very high numbers right now," Viezbicke said.
Federal officials said that may mean some animals can't be rescued.
Scientists suspect warmer than usual ocean temperatures may be making it harder for sea lion pups to get the nourishment they need. There is also a chance that an illness is causing the problem.
Federal officials said checks of the two main breeding grounds in the Channel Islands found most of the sea lion pups there are significantly underweight.
That raises the odds the young marine mammals will get into trouble when they wean off their mother's milk over the next two months.
March and April are typically the busiest months for sea lion strandings.
"We think this will continue, certainly into the spring," Sharon Melin, a wildlife biologist with the administration, said. "And the causes for the (low) weights are being investigated. We're focusing on disease, and prey availability, and diet of females."
The SeaWorld Animal Rescue Center in San Diego has received 230 struggling sea lions this year.
