Complex sentence: The mud snail was first detected in the United States in Idaho's Snake River in 1987, the mudsnail has since spread to the Madison River, Firehole River, and other watercourses around Yellowstone National Park; samples have been discovered throughout the western United States.
Split into simpler sentences: The mud snail was first detected in the United States in Idaho's Snake River in 1987. The mudsnail has since spread to the Madison River, Firehole River, and other watercourses around Yellowstone National Park; samples have been discovered throughout the western United States.