Spotting

Description:

I was unable to see underneath, but I'll go with a wild guess: Armillaria bulbosa also known as Armillaria gallica, a common wood-rot fungus. It is commonly found on weakened beech tree (which is possible here; common beech being the most widespread broad-leaved tree in Croatia forests) or ots stumps. It produces a fruit bodies of about 10 cm in diameter, yellow- to beige-brown, and covered in small scales; often depressed in center; and with a whitish stem.

Habitat:

Here, observed in Krka NP, growing on a stump of a fallen tree; the stump standing in the middle of a fast-flowing stream. The park itself is in the place where river Krka forms a series of waterfalls and lakes; it is surrounded by a magnificent dense broad-leaved forest, and its shallow coastal waters are rich in vegetation.