It was when members of the field station paddled a canoe in Tåkern during an ordinary inventory that the discovery was made.
You can hear more about how it came about and why the egret is now so far north in the video above.
The species began to breed in Sweden in 2012 and it was first discovered at Storsund on eastern Gotland.
More nests have since been found on the island and along the Småland coast, according to Tåkern's field station.
The egret has increased rapidly in number in several countries in Europe during the 2000s.
The association believes that the conditions for the species are the right ones in Tåkern and that it will therefore stay there, and increase in number.
Pictures of the species in the clip above.