Brown Trout are indigenous to most of Europe from Iceland and the UK to Turkey and south to the Atlas Mountains in Morocco. Brown Trout that live in large bodies of water whether it be land locked or the ocean, can get rather large.
The sea run Browns that ascend the Rio Grande River in Tierra del Fuego, Argentina average over 25”. Additionally, because of their propensity to live in the calmer portions of streams, they expend relatively less energy stalking food sources than for example, Rainbow Trout, and in some case grow very large.
It is not uncommon to hook into a fish as large as 30” in some rivers.