You're at 1,500 meters
The lake basin sits at roughly 1,500 m above sea level, and that altitude is the whole reason for the climate the area is known for: average temperatures described at 20–26 °C most of the year. People here like to say they have one of the best climates in the world, and after a few days you stop arguing with them.
Two practical consequences. The sun is stronger than the mild air suggests — hat and sunscreen even on a day that feels cool — and it's worth drinking more water than usual and not spending your first afternoon walking uphill in a hurry.
And the nights: at this altitude they cool off even after a warm day. Bring something with sleeves, especially in the dry season.