Sebastian - Biologists from the Florida Fish and Wildlife Conservation Commission said they believe a lack of oxygen is what caused thousands of fish to die at Sebastian Inlet State Park.

WPBF 25 News alerted the FWC after u local user jhazel uploaded photos of the dead fish that had washed ashore Friday morning.

"I saw the fish jumping out there and I thought it was going to be a really good day for fishing, and then I noticed over here in the surf that they're all dead," fisherman Jeff Johnson told WPBF 25 News.

FWC biologists arrived to assess the situation and take water samples as people watched.

"It's a little shocking, yes," Johnson said. "I don't know if there's chemicals in the water or the temperatures that caused this."

Biologists said it's neither.

"Just because there's such a large school of them, they use up the oxygen really quickly, and because they are coming closer to shore, there's not as high of a water turnover rate sometimes when you're in an area with not as much tidal flow," FWC biologist Kelli O'Donnell said.

The lack of oxygen also affected a 20-pound redfish. O'Donnell swished it through the water to get more oxygen through its gills.

Although the mass fish deaths are rare, biologists said these types of fish are prone to die from a lack of oxygen.

"There's still a huge school out there where if they don't swim away soon to go to an area where there's a higher oxygen level, then they are going to probably end up dying also," O'Donnell said.