What Animals Live In The Thames

Last Tuesday, I was walking along the South Bank, sipping a dangerously overpriced flat white, when I saw a flash of grey fur bobbing in the water. It was a seal. Not a pigeon, not a tourist, but a proper, whiskery seal, looking at me like I was the weird one for being on land. It ducked under a tourist boat and came back up with something that might have been a fish—or a discarded Greggs sausage roll, I honestly couldn’t tell. That’s when it hit me: the Thames isn’t just a grey, soupy highway for commuters. It’s a wildlife corridor, and it’s absolutely buzzing with creatures you’d never expect to see in a capital city.

So, let’s talk about who actually lives in that muddy old river. Spoiler alert: it’s not just eels and angry swans.

Seals: The Thames’s Flashiest Residents

Yes, you heard that right. Both harbour (common) seals and grey seals have decided that London is a lovely place for a holiday. In 2023, the Zoological Society of London spotted nearly 3,000 of them in the estuary. They pop up as far inland as Teddington Lock, which is basically the suburbs. (Imagine commuting from the North Sea to Richmond just to chill.)

They’re here because the water is actually cleaner than it’s been since the Industrial Revolution. They follow the fish, and the fish are following the cleaner water. It’s a whole, slimy, aquatic chain of life. You’ll see them lounging on buoy platforms like lazy teenagers, flipping their tails at passing boats.

The Underground: Crabs, Eels, and the “London Lobster”

Now, let’s get muddy. The Thames bed is crawling with crab life—specifically, Chinese mitten crabs. These guys look like they’re wearing fluffy brown mittens on their claws, which is adorable until you realise they’re an invasive species that burrows into riverbanks and causes erosion. But hey, they’re part of the crew now. They’re basically the hipsters of the Thames: arrived from Asia, wearing weird accessories, and digging up the neighbourhood.

And then there are the eels. European eels have been swimming up the Thames since Roman times. They’re born in the Sargasso Sea, travel thousands of miles, and end up in your local London canal. Tragically, they’re critically endangered now, so if you see one, consider it a tiny, noodle-shaped celebrity.

Oh, and don’t forget the smelt—a fish that smells like cucumber. I’m not kidding. Look it up. The Thames is basically a river that occasionally smells like a salad.

Birds: The Loud, Feathered Mafia

You can’t miss the mute swans. They belong to the Queen (technically, the Crown), and they know it. They hiss at you with the authority of a barrister. But there’s way more variety. Cormorants look like gothic seabirds, standing with their wings spread out to dry, like they’re posing for a dark album cover. Herons stand motionless for hours, waiting for a fish—they’re the meditation gurus of the river.

During winter, you get redshanks and curlews poking around the mudflats. They’re wading birds with long beaks, and honestly? They look a bit awkward. But they’re tough. They choose to winter in a river that has “raw sewage” in the news every other month. Respect.

Marine Mammals You Won’t Believe

Alright, brace yourself. The Thames has had whales. Not a joke. In 2006, a northern bottlenose whale got lost and swam up to Chelsea. It was a massive event—everyone went out to gawk, and sadly it died, but still! A whale! In London! There have also been dolphins spotted as recently as 2021, leaping around near Gravesend. (Gravesend: now a dolphin-watching hotspot. Who knew?)

Then there are the porpoises. Harbour porpoises are shy, small, and they pop up in the estuary fairly often. They’re like the introverts of the ocean who just want to eat fish and not be bothered by jet skis.

The Gross But Vital: Worms and Microbes

Let’s get real for a second. The Thames would be a dead zone without the tiny guys. Billions of tubifex worms live in the mud, feeding on organic waste. They’re gross—bright red, wriggling in clumps—but they’re the river’s janitors. They eat our leftover sewage so you don’t have to. Thank a worm today.

And don’t get me started on the plankton. They’re invisible to the naked eye, but they form the base of the food chain. Without them, no fish, no seals, no dolphins, no frantic Londoners spotting a beak in the water. It’s all connected, man.

Why Should You Care?

Because the Thames is healthier than it’s been in 150 years. Seriously. In the 1950s, it was biologically dead—zero oxygen, zero fish. Now, over 115 species of fish swim through it. That’s more than in the entire Rhine River. If you live in London, you’re sharing your commute with seals. That’s insane. That’s beautiful. That’s also a little terrifying when you see the size of some of those cormorants.

So next time you cross a bridge, stop. Look down. You might see a heron, a seal, or just a lot of brown water. But know that underneath that murky surface, there’s an entire, weird, wonderful ecosystem—just trying to survive the tide, the plastic, and the tourists. And honestly? They’re doing a better job at it than most of us.