Guys If fish do this it’s because they want to go and lay their eggs in a river

Guys, you’re absolutely nailing it. When you see a fish doing this – and “this” can manifest in a few awe-inspiring ways – it’s almost always driven by one of the most powerful, ancient, and undeniable urges in the natural world: the imperative to reproduce, to return to the freshwater, and lay their eggs.

Let’s talk about what “this” often looks like, and why it’s so breathtaking.

The “This” We See:

Fighting the Current Upstream: Imagine a salmon, its sleek, silver-red body straining, pushing against a furious torrent of water. It’s not drifting aimlessly; it’s deliberately aiming its nose upstream, finning with incredible power, often against currents that seem impossible to overcome. Its scales might be bruised, its fins tattered, but it will not stop.
Leaping Waterfalls and Rapids: This is perhaps the most iconic “this.” You see those incredible videos or, if you’re lucky, witness it in person: a fish, often a mighty salmon, launching itself out of the water, arcing through the air, sometimes clearing several feet, all to get over a cascading waterfall or a series of churning rapids. They launch themselves again and again, slamming back into the water, sometimes injured, but driven by an internal compass that tells them, “This is the way.”
Changing Appearance: For many species, especially salmon, their appearance transforms dramatically. Their sleek ocean silver gives way to mottled reds, greens, and browns. Males develop hooked jaws (kypes) and humped backs, making them look almost monstrous, but it’s all part of preparing for the challenge ahead – and for defending their spawning grounds.
Gathering at River Mouths: Before they even enter the freshwater, huge numbers of these fish will congregate at the mouth of rivers, tasting the freshwater, waiting for the right moment, for cooler temperatures or a heavy rain to aid their journey upstream.

Why They Do It: The Primal Call

For many anadromous fish (meaning they live in saltwater but breed in freshwater, like salmon, some trout, sturgeon, and shad), their lives are a grand cycle dictated by a biological clock.

The River of Birth: They are born in these very rivers, often high up in the headwaters, emerging from tiny eggs nestled in gravel beds. They spend their youth here, imprinting on the unique chemical signature of their natal stream.
The Ocean’s Bounty: As juveniles, they migrate downstream to the ocean, where they spend years feeding, growing large and strong, storing up incredible reserves of energy.
The Irresistible Urge: Then, as maturity hits, a switch flips. That imprinted memory becomes an overwhelming, irresistible summons. Their bodies begin to change, preparing for the epic journey. They stop feeding because they are literally running on fumes – the stored fat and energy will fuel their incredible upstream migration.
Perpetuating the Species: The goal is singular: to return to those same gravel beds, to dig a nest (a “redd”), to deposit their eggs, and for the males to fertilize them. For many species of Pacific salmon, this is a one-way trip; they will die shortly after spawning, their bodies providing vital nutrients to the river ecosystem that will nurture their offspring.

So, when you see a fish doing “this” – battling currents, leaping impossibly high, their bodies transformed – understand that it’s not a casual swim. It’s a heroic, instinct-driven epic, a testament to the raw power of nature’s will to survive and reproduce. They do it because their entire biological purpose has culminated in this arduous, magnificent journey back to the river to lay their eggs, ensuring the next generation will continue the ancient cycle.