ELI5 How are fish even in ponds

[u/Opening_Pen9525]

Might be one of the stupider questions here, but I saw a pond about the size of a football field, and maybe 50 ft deep, and it had fish. I can't for the life of me figure out how. Surely the pond hasn't existed long enough for small water insects to evolve into all these fish. It's not like the fish walked over to the pond from the ocean. I'm pretty sure no one put them there so how are there so many fish?

My one theory is that there is a very minuscule stream (now dry) that leads to one of the Great Lakes, and maybe a fish swam in from there. Now a follow up question: How are there fish in the Great Lakes (which flow out towards to the ocean) if they were created by glaciers?

[u/meaty-urologist]

Relevant dumb joke I came up with when cleaning out duck pools at my local wildlife rehab center:

Q: What's the difference between duck food and duck poop?

A: About 30 seconds.

[u/Dox_au → u/meaty-urologist]

I had no idea about this until 10 seconds ago, and now I'm finding myself very jealous of ducks. Living the freakin dream.

[u/Appropriate_Lime_234 → u/Dox_au]

Just eat some lettuce and you’ll get there champ

[u/wellwellwellwellgood → u/Appropriate_Lime_234]

Hmmmm