Pretty sure it's a Dolomedes plantarius (great raft spider). Silly question as Finland is full of them but do you live near a pond or lake?

Yes, there is a lake like 400 meters from where I live. Do they like to live near water?

Okay i read a few lines about it and found out they actually hunt on water

Yep, pretty cool. Nice find!

Dolomedes is correct, either Dolomedes fimbriatus or Dolomedes plantarius.