A drone photographer captured the concerning sight Saturday off of Palos Verdes Estates.
Mauricio Tassara estimates the whale was 30-35 feet long.
"Really big. Its pectoral fins were sticking out like a jet plane," he said.
But hidden beneath the water was a troubling and life-threatening sight. The massive mammal was trapped in a net.
"It was a thick rope that was wrapped right around the very end of its tail, right in front of the fluke. And then it draped over the right side of its fluke... That tail was bent down," Tassara added.
At first, the whale was moving very slowly, seeming to struggle to dive. Tassara followed the animal as it moved south, and at one point it seemed to suddenly come to life.
But Captain Christian Batts of Harbor Breeze Cruises, who also saw the whale, says the animal's life is at risk.
"Ultimately, this whale could pass from this entanglement. Especially with the current state of its health, with all the lice on it. That's usually a sign that it's not far from passing," Batts said.
Tassara sent his drone video to National Oceanic and Atmospheric Administration's specialized entanglement team, which is now trying to find the whale in hopes of saving its life. That's like finding the proverbial needle in a haystack. Even if they do, freeing it is extremely difficult.
"NOAA's entanglement team is very good at what they do, but even for them, it's definitely hard for these large animals."
Batts says entanglements aren't very common in Southern California. He's only seen four in the last 14 years, but the outcomes often turn fatal.
"This is the first time I've actually seen a humpback whale and it happened to be an entanglement, which broke my heart," Tassara said.
The whale hasn't been seen since Saturday. Batts says it's possible it headed off shore or back up north. If anyone spots the animal, they are urged to contact NOAA's entanglement team.