"The tidal reaches of the Thames constitute a badly managed open sewer," reported The Guardian in 1959. "No oxygen is to be found in it for several miles above and below London Bridge."

The river, which winds through the heart of one of Europe's biggest cities, was declared biologically dead in 1957. In the years since, its churning brown waters have been written off as dirty and toxic. 

So, scientists from the Zoological Society of London were astounded when they found more than 1,000 seals lounging on the banks of the Thames estuary.

"The seals would not be able to pup here at all without a reliable food source, so this demonstrates that the Thames ecosystem is thriving," said conservation biologist Thea Cox.

Delicious grub up for grabs includes 115 different types of fish, two species of shark, short-snouted seahorses and the European eel, which is critically endangered. 

The seals have competition from other Thames residents, including porpoises, dolphins and visitors like Benny the beluga whaleBenny lived in the Thames for around three months from September 2018, before heading home to the Arctic Ocean.. 

Elsewhere, there is more good news: across the British countryside, goldfinches and wood-pigeons can be heard twittering once again. The number and variety of birds in Britain is rising after years of decline.

And further afield, scientists detected that the song of blue whales has been dropping in pitch across the world. They were puzzled: was it a side-effect of the climate crisis? But no: they now believe that blue whale numbers are growing, so whales no longer need to strain their voices to be heard.

Today, news about the natural world can be relentlessly awful. Earth is in the midst of its sixth mass extinctionThe fossil record shows there have been five mass extinctions, including the asteroid strike that wiped out the dinosaurs. This time, human are responsible for the dramatic drop in biodiversity.. Humans have wiped out over half of the planet's animals since 1970. But, now, there are some rays of light in the gloom. 

Yes: In its long and tumultuous history, the Earth has faced many moments of peril. But life always finds a way to adapt and rise again. The return of the Thames from the dead is proof. 

No: Our era is unprecedented. We are radically changing the chemical composition of Earth's atmosphere. The Thames's fish have bellies full of microplasticsMicroplastics are fragments of degraded plastic that are less than five millimetres in length. They are blown into the atmosphere and transported by ocean currents. . And right now, the Amazon is disappearing. 

Or... We cannot be complacent. Nature does not just heal by magic. If some animals are recovering, it is thanks to dedicated and longstanding conservation efforts.