Currently, there are brown trout in almost every state in the Continental US, yet every single one of them can trace its routes across the Atlantic Ocean.
Brown trout are originally native across a large portion of Europe and western Asia. In the 1800s, Europeans began farming brown trout for food and to support recreational fishing. The availability of brown trout eggs and fry led to the introduction of brown trout in colonial areas around the world, so that the Europeans living there would have some familiar recreation and food source to enjoy. It was during this time period and onwards that brown trout were introduced to the United States, as well as Australia, New Zealand, India, Patagonia, and parts of Africa.
The first American brown trout were introduced to Michigan and New York in 1883 through two fish hatcheries. They came mainly from a German strain of eggs, and old timers will sometime refer to brown trout as “German trout” in the US. They were thought to be particularly valuable because they grow faster and can withstand higher water temperatures than rainbow or brook trout, and therefore made sense for aquacultural purposes.
For many native American trout, such as the Appalachian brook trout or the Westslope cutthroat, competition and hybridization with introduced brown trout has put some serious stress on indigenous populations. Brown trout tend to grow faster and be more aggressive than rainbow and brook trout, so they outcompete the rainbows and the brooks for limited resources. When they get big enough, brown trout are known to prey directly on smaller trout, which explains all those massive streamers you have in your fly box. Hybridization between brown trout and brook trout is also an issue, but can sometimes create something really cool looking called a tiger trout.
While there is no such thing as a strictly native brown trout in the States, many of America’s brown trout populations have become incredibly naturalized and essentially completely wild. They look and behave exactly like a wild fish would.
As anglers, it’s kind of weird to think about brown trout as an “invasive species”, although strictly speaking they technically are in the US. Either way, they are undoubtedly some of the most fun and beautiful fish in the river.