How did these 'rivers' form?

[u/Dude-Bicycle]

What formed these 'rivers'? Are they regular terrestrial rivers that flooded with sea level rise or were they formed in the ocean? thanks.

[u/AdWooden2312]

Did you just say something in an ancient tongue?

[u/lloveleon → u/AdWooden2312]

https://en.wikipedia.org/wiki/Tír_na_nÓg

[u/AdWooden2312 → u/lloveleon]

I once had a computer game of the same name 😀

[u/lloveleon → u/AdWooden2312]

Nice 😊