Several years ago I worked in housing. In that job I was responsible for looking after abandoned properties among other things.
One day I had to go out and inspect a house. It was full of belongings which was very difficult to get through because furniture was strewn everywhere. So I did an inventory and arranged for it to be cleared. I took photos, and when I reviewed them I saw a very green fishtank. The property had apparently been empty for two months before we were notified it was empty, but something prompted me to contact the team who were due to clear the house and asked them to look for it.
It turned out there was a goldfish in the tank! Not visible because of the algae in there. Luckily it had been eating the algae. It was rehomed to a garden fishpond.