Cortinarius lacustris

Cortinarius lacustris is an inedible species of mushroom-forming fungus belonging to the family Cortinariaceae and found mainly in oak groves in deciduous forests.

Description
The mushroom cap is a reddish, cinnamon brown with a diameter between 2–5 cm. It has a cylindrical stipe] that turns to a purple-black when reacting to potassium hydroxide solution exposure. The partial veil has a slight yellow colour. The ellipsoid spores measure between 8.5–11 μm by 5–6 μm.