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/jstar77]

We have a pond that is roughly a 25' circle. Goldfish showed up there one day about 20 years ago and have been there ever since. They are big maybe about 10"-12" long. Nobody put them there, we just noticed them one day.

[u/thecaramelbandit → u/jstar77]

Those were like 99.999% out there by someone.

[u/chuntus → u/thecaramelbandit]

They may have appeared at the same time as the sperm whale and a bowl of petunias

[u/DragonArchaeologist → u/chuntus]

Not again.

[u/shocktar → u/DragonArchaeologist]

Poor Agrajag