Tomo the sea lion caused quite a stir when she showed up in front of the Catholic church in Tomales last week, far from the ocean. After a valiant rescue by the Marine Mammal Center and a ragtag team of townsfolk, her story was supposed to have a happy ending.

It didn’t.

She was discovered last Monday morning, sunning herself on a concrete wall in front of the Church of the Assumption rectory, five feet above the sidewalk on Highway 1, bewildering passersby. She was a good three or four miles from Tomales Bay and Dillon Beach.

“I’ve had interesting calls over the years, but I’ve never seen a sea lion along Highway 1 before,” said Capt. Tom Nunes, who was on duty at the Tomales Fire Station when Tomo caused a kerfuffle.

Neither had Bill Jensen, a fifth-generation rancher who has lived in town for all his 73 years.

“There she was, sitting right there,” he said, pointing at Tomo’s perch a couple days later. “Crazy. Just crazy.”

Both men participated in a successful rescue of Tomo, who put up a struggle before she could be ushered into a crate and taken to the Marine Mammal Center’s hospital in Sausalito for an evaluation. They assumed she would soon be back in the water, behaving like a normal sea lion with a better sense of direction.

But the next day, when veterinarians examined Tomo, a three-year-old female weighing 115 pounds, they observed signs of domoic acid poisoning. Domoic acid is a neurotoxin produced by algae blooms often referred to as red tides. 

“It’s a naturally occurring toxin in the water that builds up through the food chain,” said Giancarlo Rulli, the center’s spokesman. “If it is in the body of the sea lion for a long period of time, it causes disorientation and seizures and can cause permanent brain and heart damage.”

The worst part? “There’s no way for them to flush the toxin out of their body,” Mr. Rulli said.

The Marine Mammal Center has encountered many cases of domoic acid poisoning over the years. Last summer, after an algae bloom off the coast of San Luis Obispo, it responded to over 200 suspected cases among sea lions during a two-month period.

Last Wednesday, two days after she was admitted, Tomo showed the telltale signs of chronic exposure. She was twitching and having seizures. She was lethargic and disoriented. The veterinarians concluded that she was unlikely to survive at sea, and they decided to euthanize her.

That outcome took Mr. Jensen by surprise, given Tomo’s behavior during her capture, when she put up vigorous resistance as the team attempted to capture her with a net.

“She put up a helluva struggle,” he said. “She was pissed off and swinging her head in every direction and biting at the net.”

Positioning the crate wasn’t easy, given her precarious location. But two trained volunteers mapped out a plan and directed others who arrived at the scene, including Mr. Jensen and Eric Knudsen, another Tomales resident who had come to gawk. They were assisted by Capt. Nunes and two other Tomales firefighters who arrived in a fire truck to find an officer from the California Highway Patrol directing traffic around the site.

One of the rescue center volunteers was Cathy Schwemm, a retired wildlife biologist and Tomales resident who was astonished when she received an alert about a sea lion in town. She called the center to confirm that it wasn’t a hoax.

“You’re joking, right?” she asked the person who answered the phone. “There’s not a sea lion in Tomales.”

“Yes, there’s a sea lion in Tomales,” the woman replied.

Ms. Schwemm went to scope out the situation and brushed past Tomo without realizing it. Her location on the wall was obscured by a bush, and Ms. Schwemm couldn’t see her when she started down the stairs. She was startled by a growl and immediately backed away. 

“You don’t want to get that close at all, but I just didn’t see it, and I had no idea,” she said. “I didn’t think it was going to be right by the street. If I had been looking the other way or not paying attention, she could have lunged right at me. They have very big teeth. That’s how they eat their fish.”

The second trained volunteer, who also lives nearby, Amy D’Ambrogia, drove to Bodega Bay to retrieve a rescue center truck equipped with a crate and the wooden shields that the teams use to guide pinnipeds in the right direction. 

Ordinarily, six to eight volunteers show up to conduct rescues, but it was Monday morning, people were busy, and a full team could not be assembled. If Tomo had been stranded on the beach, they might have simply put up a sign warning people to keep their distance until help could arrive.

“This guy could not stay here,” Ms. Schwemm said. “It was just a dangerous situation. If somebody walks by with a little dog and this big sea lion is up there, it might not go too well.”

With Ms. D’Ambrogia directing them, the untrained volunteers did their part. They guided Tomo to the door of the crate, and as Mr. Jensen lifted the back of the net, she slid out with no place else to go.

“It was great,” Ms. Schwemm said. “They were very good.”

The makeshift crew celebrated their work and assumed the best as the truck headed off to the hospital.

“Everybody was speculating about what happened,” Mr. Jensen said. “How did this thing possibly get here? My theory is, she found some steelhead or coho that were migrating up Walker Creek and chased them right here.”

The creek eventually empties into a tributary about a quarter-mile behind the church. From there, Tomo would have had to wriggle her way up a grassy hill to the rectory—or flop her way up Highway 1.

Either way, she would have made her way past the long-haired Scottish highland cattle and grazing sheep in the emerald pastures of Longmeadow Ranch, where Mr. Jensen is the caretaker.  

“I believe an animal like that would go over wet grass,” Mr. Jensen speculated. “I don’t believe she’s going to go over the pavement like a pedestrian.”

There was a king tide the night before, so the creeks were high and the pastures were swampy.

“She ran out of water, and it’s like, ‘Where now? I’m going to go looking.’ She’d probably never embarked on anything like this before, so she didn’t have the savvy to turn around and go back to saltwater.”

Mr. Jensen didn’t learn about Tomo’s fate until this week, and he was surprised to hear of her passing. “Well, it’s too bad,” he said. “Tomo didn’t make it.”