I leave the question of the owls for Kalle to answer. ;)
Kind regards,
And I'm sure there are owls there, they are everywhere in Sweden! :) But that lake, Öllesjön, I have a theory. Vowels change more than other parts of words, and it might not have been Ö allways. What if it was once Alesjön, or Ällesjön? Al is the swedish name for the tree Alder, a wetland tree growing in riparian areas all over the country. And a group of alders was called "Ale" or "Äle" or even "Älle". There is even a farm in Hällaryd parish that is called "Ällestad". Stad means place and Älle means a stand of alder trees.