The surviving swan from the Palace of Fine Arts lagoon, Blanche, was returned to her home on Tuesday after being treated at the San Francisco Zoo for several weeks for lead and zinc poisoning.

Her mate, Blue Boy, died somewhat mysteriously last week while he was also at the zoo, despite not showing the same symptoms as Blanche and not seeming ill until right before his death. Both swans were found to have high levels of zinc and lead in their blood, but it remains unclear whether this contributed to Blue Boy's death — a necropsy is still pending, as Rec & Parks spokesperson Tamara Aparton tells KTVU.

Zinc poisoning is fairly common among birds, according to zoo veterinarians, because birds like these pond-floating swans tend to swallow pennies and other coins that people toss in the water for good luck. The source of the lead in their systems is believed to have possibly come from a buildup after consuming soil in the area for years — which has trace amounts of lead in it, as most soil in urban areas does.

Rec & Parks officials conducted multiple soil samples around the lagoon, and reportedly some areas had higher levels of lead than others.

Blanche and Blue Boy were mates for the last ten years, and as Aparton tells KTVU, "I’m sure she is missing him, as swans mate for life." Blue Boy came to the lagoon from New York around the age of 7 — his age seems to have been something of a moving target, as vets said he was 17 when he died, but reports on the first brood of cygnets he had with Blanche in 2011 suggested he was 2 at the time, so the math is off somewhere.

This is not the first time that Blanche has been left alone in the lagoon following a tragedy. Blanche's five-year-old sister, Monday, was killed by a vandal in November 2010 — her neck was snapped and she was found floating in the water — and this was not long after Blanche's 19-year-old mother, named Friday, was stolen out of the lagoon. There was also a sister named Wednesday, but I'm not finding a record of what happened to her.

Blanche is unlikely to find another mate even if news swans are brought to the lagoon. And she's getting up in years — at age 25, she likely only has a few more years left in her. She had her last offspring over five years ago — the last eggs she laid in 2014 were removed and replaced with ceramic ones, to fool her, because Rec & Parks said at the time, "We just can't have any more cygnets." The males got aggressive, and there were battles for dominance that sometimes ended with one dead, possibly at the hands of his father. Also, in years past, coyotes and other predators have eaten Blanche's progeny.

Rec & Parks would like everyone to stop throwing coins in the lagoon, and no one should be approaching Blanche (it stresses her out) or trying to feed her if you see her out there. Gayle Haggerty, the "Swan Lady" volunteer who's been caring for the birds for the last 25 years, will be following vets' advice and not feeding Blanche directly off the ground anymore, to keep her from ingesting any unnecessary dirt.

Anyway, below is the bittersweet clip of Blanche returning to her longtime home, all alone, on Tuesday.

Previously: Blue Boy, One of the Two Swans at the Palace of Fine Arts Lagoon, Has Died From Zinc and Lead Poisoning